I'm about to push this car off of a cliff... any help would be greatly appreciated!
#1
08-30-2016, 05:11 PM
I'm about to push this car off of a cliff... any help would be greatly appreciated!
I have what seems to be the worst "perfect storm" of problems I've seen on my 95 Jimmy so far. Recently I have been having HVAC issues, and braking issues, so I did the necessary things to fix what I thought were the problems. For the brakes I have replaced all brake pads, front calipers, rotors, and master cylinder and did a whole lot of bleeding. For my HVAC I have replaced the blower motor, resistor, control panel, checked fuses, relays, and tried to check vacuum lines.
Things were working great with the brakes for a little bit, but I never resolved the HVAC issue that I had which was no pressure a/c or heat. It was just "leaking" air, but wouldn't blow. My HVAC problem was still in the works, but then driving on the highway yesterday I had a near brake failure. I was pushing the brake all the way to the ground, and not getting any stopping pressure. I pretty much coasted to a stop. The brake light appeared on the gauge cluster, and it is only on when I'm not braking. If i pump the brakes for a while, and then drive it stays off, but with just regular driving it is always on. I was thinking it was possibly a power brake booster failure, but i'm not sure...
I have also had a high idle for a little while, and I think it might be vacuum related too. I decided to check for vacuum leaks again, and the only place where I could raise my idle with starter fluid was around the egr valve. It is close to the intake manifold gasket too, so it could possibly be there. Would a leak like that cause constant high idle, and also brake issues like I experienced? In park I am at a constant 2,000 rpm's, and when I'm in drive it is a bit lower, but I don't really have to push on the accelerator to coast. It is like cruise control.
So, I obviously have several problems, but there is a chance that they could all be vacuum related. There is still vacuum pressure, but maybe not enough?
Any helpful comments for any of the above problems would be appreciated, thanks!
Things were working great with the brakes for a little bit, but I never resolved the HVAC issue that I had which was no pressure a/c or heat. It was just "leaking" air, but wouldn't blow. My HVAC problem was still in the works, but then driving on the highway yesterday I had a near brake failure. I was pushing the brake all the way to the ground, and not getting any stopping pressure. I pretty much coasted to a stop. The brake light appeared on the gauge cluster, and it is only on when I'm not braking. If i pump the brakes for a while, and then drive it stays off, but with just regular driving it is always on. I was thinking it was possibly a power brake booster failure, but i'm not sure...
I have also had a high idle for a little while, and I think it might be vacuum related too. I decided to check for vacuum leaks again, and the only place where I could raise my idle with starter fluid was around the egr valve. It is close to the intake manifold gasket too, so it could possibly be there. Would a leak like that cause constant high idle, and also brake issues like I experienced? In park I am at a constant 2,000 rpm's, and when I'm in drive it is a bit lower, but I don't really have to push on the accelerator to coast. It is like cruise control.
So, I obviously have several problems, but there is a chance that they could all be vacuum related. There is still vacuum pressure, but maybe not enough?
Any helpful comments for any of the above problems would be appreciated, thanks!
#2
08-30-2016, 11:17 PM
Most of what you described sound like it could be vacuum related but not the brakes. Without vacuum you brake pedal would be very, very stiff. Sounds like you have air in the lines or a leak somewhere for the brakes.
#3
08-30-2016, 11:28 PM
Thanks for the reply, I bled the brakes again and there was no air in the lines, I also haven't lost any fluid from the master cylinder.. so I don't think it is a leak. I've heard that there is a way to do a bleed cycle witj a special tool on the abs module... would not doing that create that bad of a problem. There shouldn't be any air in that.
I checked all of the vacuum lines with a gauge and everything going to components under the hood is leak free, but the 3 lines going through the firewall into the dash wouldn't hold. Is there an easy way to get to those?
#4
08-31-2016, 07:22 AM
Thanks for the reply, I bled the brakes again and there was no air in the lines, I also haven't lost any fluid from the master cylinder.. so I don't think it is a leak. I've heard that there is a way to do a bleed cycle witj a special tool on the abs module... would not doing that create that bad of a problem. There shouldn't be any air in that.
I checked all of the vacuum lines with a gauge and everything going to components under the hood is leak free, but the 3 lines going through the firewall into the dash wouldn't hold. Is there an easy way to get to those?
I checked all of the vacuum lines with a gauge and everything going to components under the hood is leak free, but the 3 lines going through the firewall into the dash wouldn't hold. Is there an easy way to get to those?
It is common for the vacuum reserve tank for the HVAC to get unplugged. It is inside of the fender on the drivers side near the firewall on my 2001, but I don't know where it is on a 1995. However, I really doubt if this is the reason for a high idle, as the IAC motor should slow it down.
#5
08-31-2016, 04:52 PM
If you get air in the abs system, as you undoubtedly did - then the only way to bleed the ABS module is using a capable scan tool to trigger the fuction in the vehicle's PCM. Trick is to never let the ABS system go dry.
It is common for the vacuum reserve tank for the HVAC to get unplugged. It is inside of the fender on the drivers side near the firewall on my 2001, but I don't know where it is on a 1995. However, I really doubt if this is the reason for a high idle, as the IAC motor should slow it down.
It is common for the vacuum reserve tank for the HVAC to get unplugged. It is inside of the fender on the drivers side near the firewall on my 2001, but I don't know where it is on a 1995. However, I really doubt if this is the reason for a high idle, as the IAC motor should slow it down.
#6
08-31-2016, 11:47 PM
Alright, so I think I have the brake issue taken care of. I couldn't find a shop with a tech 2 scanner, and the gmc dealer service center didn't answer, so I decided to try another fix for the abs, which is driving it on a dirt road and slamming the brakes a lot so that the system purges out any air. Following that the lines were bled again. Brakes done.
There is no leak at the vacuum reserve, the only traceable leaks are behind the dash and hard to get to... I'm also not sure where exactly. Is one of the actuators known for vacuum failure by chance?
I cleared my codes a few days ago and today the light came back on. I scanned it and it said it was iac valve failure or fuel pressure too high. I switched out the iac valve and cleaned my throttle body and still have a very high idle just over 2,000. What else could be the problem?
There is no leak at the vacuum reserve, the only traceable leaks are behind the dash and hard to get to... I'm also not sure where exactly. Is one of the actuators known for vacuum failure by chance?
I cleared my codes a few days ago and today the light came back on. I scanned it and it said it was iac valve failure or fuel pressure too high. I switched out the iac valve and cleaned my throttle body and still have a very high idle just over 2,000. What else could be the problem?
#7
09-01-2016, 07:19 AM
Alright, so I think I have the brake issue taken care of. I couldn't find a shop with a tech 2 scanner, and the gmc dealer service center didn't answer, so I decided to try another fix for the abs, which is driving it on a dirt road and slamming the brakes a lot so that the system purges out any air. Following that the lines were bled again. Brakes done.
There is no leak at the vacuum reserve, the only traceable leaks are behind the dash and hard to get to... I'm also not sure where exactly. Is one of the actuators known for vacuum failure by chance?
I cleared my codes a few days ago and today the light came back on. I scanned it and it said it was iac valve failure or fuel pressure too high. I switched out the iac valve and cleaned my throttle body and still have a very high idle just over 2,000. What else could be the problem?
There is no leak at the vacuum reserve, the only traceable leaks are behind the dash and hard to get to... I'm also not sure where exactly. Is one of the actuators known for vacuum failure by chance?
I cleared my codes a few days ago and today the light came back on. I scanned it and it said it was iac valve failure or fuel pressure too high. I switched out the iac valve and cleaned my throttle body and still have a very high idle just over 2,000. What else could be the problem?
https://blazerforum.com/forum/diagno...plained-35140/
Display IAC position or IAC counts on your scanner when the idle is stuck above 2000. Please report.
Last edited by LesMyer; 09-01-2016 at 07:37 AM.
#8
09-01-2016, 07:53 AM
Additional Info for you
-------------------
Idle Air Control Valve (IAC)
The IAC valve GM uses for most of their engines is a stepper motor actuated valve. A stepper motor is a device that moves a predetermined amount per electrical signal it receives by whatever device is controlling it. The GM IAC has a pintle that extends or retracts into or out of an idle (bypass) air passage in a throttle body or intake manifold attached to the engine. Typically as the IAC’s pintle extends, air flow to the engine is restricted as the air passage is shut off. As it retracts, air flow to the engine is increased as the air passage is opened up. This air passage is a simple bypass for incoming air to take around the throttle blade.
Diagnosing problems associated with the IAC aren’t simple. There are many other causes that can make a IAC valve appear faulty. In many cases, there may only one or two trouble codes in the ECM/PCM assigned to the IAC, but these trouble codes can set for a variety of reasons. Basically, this trouble code sets if the ECM cannot make the engine idle at a set (desired) speed by control of the IAC valve’s position. There are limits set up within the ECM that only allow it to move the IAC in and out of the idle air passage so far. The IAC valve position is referred to as IAC counts. Scan tool data indicating “0” IAC counts means the IAC valve is fully extended (shutting off idle airflow to the engine); and “255” IAC counts means the IAC valve is fully retracted, allowing as much air to enter the engine via the throttle bypass passage as possible. Some ECMs may never allow the IAC to reach 255 counts. Generally, anything you see over 160 counts should be considered to be a near- or fully-open idle air passage.
On a normal operating engine, it is typical to see high IAC counts (100 or more) when the engine is idling cold and during the warm-up cycle. As the engine warms, the IAC counts should decrease. By the time the engine reaches operating temp (fully warmed up), the IAC position should drop into the range of about 20-50 counts in park or neutral. If the scan data you get reports counts lower than this, then that can indicate one or more of the following problems exists:
· There is a vacuum leak allowing unmetered air to enter the engine
· The throttle stop screw is adjusted incorrectly (throttle being held open too far; more on this later)
· There is a problem with the throttle cable or cruise control system that isn’t allowing the throttle to close all of the way
· The IAC valve itself is faulty
Now if you see the scan data reporting IAC position higher than 20-50 counts on a fully warmed up engine, this could indicate one or more of the following problems exist:
· There is carbon buildup on the IAC pintle, or in the idle air passage restricting air flow
· There is carbon buildup on the throttle blade or throttle body bore
· The throttle stop screw is adjusted incorrectly (throttle resting closed too much)
· There is a mechanical problem with the engine resulting in lower than expected vacuum levels at idle (this will require the IAC to open further so the engine gets the required amount of air to maintain the preset idle speed)
· There is increased load on the engine (such as what would occur if the automatic transmission was shifted into gear)
· The IAC valve itself is faulty
Any one of the above issues can cause a an IAC fault code to set in the ECM. As you can see, there are many issues other than a faulty IAC valve that can cause a code to set. So before replacing the IAC valve, you should check all of these possible issues first.
The IAC valve cannot be tested using conventional electrical testing means. There are special tools available that are designed to test GM IAC valves, but I have discovered most shops don’t have these tools anymore. To be quite honest, you don’t really see many IAC valves fail. When they do, they usually freeze up or get stuck in a fixed position.
The ECM “resets” the IAC valve when the car is operated at normal road speeds (35mph or more). During this time, the IAC valve is typically extended out all the way (IAC counts = 0), thus closing off the idle air passage. This helps the ECM “learn” the position of the IAC valve. Any time the IAC valve is replaced, this “learn” procedure should be performed.
-------------------
Idle Air Control Valve (IAC)
The IAC valve GM uses for most of their engines is a stepper motor actuated valve. A stepper motor is a device that moves a predetermined amount per electrical signal it receives by whatever device is controlling it. The GM IAC has a pintle that extends or retracts into or out of an idle (bypass) air passage in a throttle body or intake manifold attached to the engine. Typically as the IAC’s pintle extends, air flow to the engine is restricted as the air passage is shut off. As it retracts, air flow to the engine is increased as the air passage is opened up. This air passage is a simple bypass for incoming air to take around the throttle blade.
Diagnosing problems associated with the IAC aren’t simple. There are many other causes that can make a IAC valve appear faulty. In many cases, there may only one or two trouble codes in the ECM/PCM assigned to the IAC, but these trouble codes can set for a variety of reasons. Basically, this trouble code sets if the ECM cannot make the engine idle at a set (desired) speed by control of the IAC valve’s position. There are limits set up within the ECM that only allow it to move the IAC in and out of the idle air passage so far. The IAC valve position is referred to as IAC counts. Scan tool data indicating “0” IAC counts means the IAC valve is fully extended (shutting off idle airflow to the engine); and “255” IAC counts means the IAC valve is fully retracted, allowing as much air to enter the engine via the throttle bypass passage as possible. Some ECMs may never allow the IAC to reach 255 counts. Generally, anything you see over 160 counts should be considered to be a near- or fully-open idle air passage.
On a normal operating engine, it is typical to see high IAC counts (100 or more) when the engine is idling cold and during the warm-up cycle. As the engine warms, the IAC counts should decrease. By the time the engine reaches operating temp (fully warmed up), the IAC position should drop into the range of about 20-50 counts in park or neutral. If the scan data you get reports counts lower than this, then that can indicate one or more of the following problems exists:
· There is a vacuum leak allowing unmetered air to enter the engine
· The throttle stop screw is adjusted incorrectly (throttle being held open too far; more on this later)
· There is a problem with the throttle cable or cruise control system that isn’t allowing the throttle to close all of the way
· The IAC valve itself is faulty
Now if you see the scan data reporting IAC position higher than 20-50 counts on a fully warmed up engine, this could indicate one or more of the following problems exist:
· There is carbon buildup on the IAC pintle, or in the idle air passage restricting air flow
· There is carbon buildup on the throttle blade or throttle body bore
· The throttle stop screw is adjusted incorrectly (throttle resting closed too much)
· There is a mechanical problem with the engine resulting in lower than expected vacuum levels at idle (this will require the IAC to open further so the engine gets the required amount of air to maintain the preset idle speed)
· There is increased load on the engine (such as what would occur if the automatic transmission was shifted into gear)
· The IAC valve itself is faulty
Any one of the above issues can cause a an IAC fault code to set in the ECM. As you can see, there are many issues other than a faulty IAC valve that can cause a code to set. So before replacing the IAC valve, you should check all of these possible issues first.
The IAC valve cannot be tested using conventional electrical testing means. There are special tools available that are designed to test GM IAC valves, but I have discovered most shops don’t have these tools anymore. To be quite honest, you don’t really see many IAC valves fail. When they do, they usually freeze up or get stuck in a fixed position.
The ECM “resets” the IAC valve when the car is operated at normal road speeds (35mph or more). During this time, the IAC valve is typically extended out all the way (IAC counts = 0), thus closing off the idle air passage. This helps the ECM “learn” the position of the IAC valve. Any time the IAC valve is replaced, this “learn” procedure should be performed.
#9
09-01-2016, 10:47 PM
Thank you for all of your replies, it is very helpful.
This evening I decided to replace my iac and check all of my sensors that could mess with the idle, they all tested fine and after turning my car on with the new valve it still had the exact same idle. I switched back to the old one and then read your new posts. I wasn't aware that I had to drive to 35mph to reset the valve, so I put the new one back in, and then took it for a drive.
I drove down my street at 25 and it behaved the same, got it up to 35 for the first time and it acted the same (not how it was supposed to, but the same high idle i'm used to now). After turning a couple of times and getting up to 35 for the second time the idle slowly progressed and got higher, it got up to 3500 - 4000 so i hurried and pulled over and shut my car of. I quickly checked for a code, and didn't see a new one and then tried to start it. It would turn over but WILL NOT START! I switched back to my old iac and tried again and it still won't start. I have unplugged, replugged, waited, and done anything that I can think of and it won't start. The fuel pump primes when I turn the key, everything behaves like normal, but I can't get the engine to start.
Does anyone have any idea what is going on???
Sorry I don't have the iac position or counts, i don't have a scanner capable of that.
This evening I decided to replace my iac and check all of my sensors that could mess with the idle, they all tested fine and after turning my car on with the new valve it still had the exact same idle. I switched back to the old one and then read your new posts. I wasn't aware that I had to drive to 35mph to reset the valve, so I put the new one back in, and then took it for a drive.
I drove down my street at 25 and it behaved the same, got it up to 35 for the first time and it acted the same (not how it was supposed to, but the same high idle i'm used to now). After turning a couple of times and getting up to 35 for the second time the idle slowly progressed and got higher, it got up to 3500 - 4000 so i hurried and pulled over and shut my car of. I quickly checked for a code, and didn't see a new one and then tried to start it. It would turn over but WILL NOT START! I switched back to my old iac and tried again and it still won't start. I have unplugged, replugged, waited, and done anything that I can think of and it won't start. The fuel pump primes when I turn the key, everything behaves like normal, but I can't get the engine to start.
Does anyone have any idea what is going on???
Sorry I don't have the iac position or counts, i don't have a scanner capable of that.
#10
09-02-2016, 07:28 AM
If it won't start then you have to go back to the basics. Fuel, spark, compression.
I may have misled you some. 1995 would be OBD1 and links/info I gave was for OBD2.
Very strange problem. If the throttle is closed and the IAC is closed - then where is the air for 4000rpm coming from? Seems either huge vacuum leak or major problem with an intake valve (second is highly doubtful). I did have an old flathead ford have a chunk of an intake valve come off and munch a hole in the piston - it the sucked air out of crankcase past the broken valve and fed the other cylinders to a surprising speed. But it also smoked pretty badly. How it got any fuel out of the carb was beyond me.
I may have misled you some. 1995 would be OBD1 and links/info I gave was for OBD2.
Very strange problem. If the throttle is closed and the IAC is closed - then where is the air for 4000rpm coming from? Seems either huge vacuum leak or major problem with an intake valve (second is highly doubtful). I did have an old flathead ford have a chunk of an intake valve come off and munch a hole in the piston - it the sucked air out of crankcase past the broken valve and fed the other cylinders to a surprising speed. But it also smoked pretty badly. How it got any fuel out of the carb was beyond me.