Hello Everybody,

I just finished a whole lot of work on my 1997 Blazer.
It deserved it after nearly 20 years.
New Upper and Lower Intake Gaskets.
New EGR Valve
New Updated Fuel Injectors.
New Idle Air Control Valve.
New Map Sensor.
New Water Pump + New Hoses
New Power Steering Pump + Hoses
New Updated Valve Covers.

The work went smooth and everything went on OK.

I have a slight problem with a High Idle.
I can be going down the road at 30-50 mph and
can take my foot off the acelarator pedal and the vehicle will
continue on as if it is on cruise control at about 1200 RPMs.
Once I hit the brake and hold it it takes about 5-8 seconds before the idle
will start to come down to normal. I have to keep my foot on the brake
in order for it to go down to normal idle (650-700 Rpms). It will not cruise
down naturally by itself.

My research tells me since I did so much work on it that the computer
is confused on the new setup. I took off nearly 20 years of carbon
on the Throttle Body and Lower Intake.

I don't think there is any thing wrong with the new parts.
Will the high idle settle down after a while or do I need the PCM
looked into having a Relearn done to it. I have read that the PCM might relearn
how to adjust to the changes over 250-300 miles once it gets use to my driving. Does anybody have any knowledge on this.
I did get a Code. P0507. Idle Air Control Unexpected High Idle.
I will double check all my connections but my gut tells me the computer could be confused
and has to adjust.

Thanks for any input/info,

Mark

 

If you are getting p0507, then it is probably not a relearn. At least that is what I think. I just went thru a P0507 issue myself with the same "cruise" issue and slow idle correction coming to a stop, on a new-to-me Jimmy. I had just rebuilt the heads and put in new gaskets. After cleaning the TB and IAC valve, checking all the usual places for vac leaks, EGR valve and Purge valve, IAC valve circcuits, My Ah-ha moment was when I backed off the idle stop set screw about 1/2 turn on the throttle body.


If you have a scanner, you might check the "Desired idle speed" vs the actual engine RPMs. This is where I found that the 2 did not match each other. No malfunctioning controls, no throttle cables hanging up, and no vac leaks meant something else was wrong. I now find the idle wants to be ~ 600 RPM, not 700 as you suggest. Once I backed off the set screw, the engine behaves both on the road and coming to a stop. and the RPMs at idle now match the "expected idle speed". Further, no more P0507 code.

 

The IAC can be reset, but it requires a bi-directional scan tool. The only "relearn" is for the crankshaft position sensor. It must be performed with a capable scan tool if/when the crankshaft position sensor and/or timing cover is moved, removed, replaced, or disturbed in any way.

EDIT: Just an FYI, Adjusting the throttle stop screw is not recommended. It is adjusted at the factory during engine assembly. Adjusting it in the field will mask the root cause of the high idle. NOWHERE in the GM dealer issue shop manual does it tell how to adjust it.

 

Thanks for the replies.
I don't have a bi directional scanner.
I saved the old one which was probably still good. I thought I was doing the old
girl a favor by putting on a new one on( Delphi). I will clean off the old one
and will be putting it back on in a week or two. Do you think the brand has anything to do
with the high idle? AC Delco Versus Delphi.

Thanks,
Mark

 

I just checked, You are right. The factory service does not say anything about the TB stop screw. However, after checking ALL other possibilities, And seeing 0 counts on the IAC and still the RPM was higher that commanded, what else was I to do? Who knows who might have adjusted it over the last 14+ years on my car. I can't ignore that, even if the book never mentions it. Plus, it worked for me. The IAC when warm is around 20 counts and changes slightly with electrical load changes. It is as high as 120 counts when cold starting in 30 deg weather.


His idle speed is ~100-150 PRM higher than it should be, even when it settles down. This means extra air is getting in somewhere. This is why I suggested querying the OBD2 port for actual vs expected RPM. This can be done with the cheap Bluetooth OBD scanners and either Torque (android) or TouchscanPro (Windows based computer) and the right PID definitions. They can also read the IAC counts. If the IAC is 0 and the RPMs do not match, then what........?????

 

If I suspect the stop screw has been tampered with on a vehicle, here's what I have done, with very good results:

#1 Bring the engine up to normal operating temp, closed loop, trans in park or neutral.
#2 Command the IAC to zero counts.
#3 Adjust the idle stop screw so rpm is 250 to 300.

When you're done, the fuel trim cell should be 17, idle speed should be 650rpm, and the IAC counts should be 18, (these are the normal specified values). If not, there's another problem somewhere, (air intrusive, etc, etc).

Also, as a quick check, If you command the IAC to 18 counts, and rpm is NOT 650, you KNOW there's a problem somewhere.

 

Well I have a new problem. Not sure if it is related to the Idle Air Control Code P0507.
After 3 glorious days of driving I had a misfire on Cylinder 2. The Service Soon Light started Flashing. I pulled to the side and put my scanner on it. Crap P0302. It was running terribly, stumbling and I crawled a little farther. I had it towed to my friend who is a mechanic. He seen the same thing I saw. Flashing Service Soon Light at Idle and a stumbling Idle/Vehicle.
He calls me this morning and says he did nothing and the car started up just fine and is running near perfect. What gives?? Is the New Injection System not trust worthy. I am not familiar with the reliability of the New AC Delco Electronic Injectors. I just know they cost a pretty penny. ACDELCO Part # 217-3028

Can anybody comment. This is only the second time I have had a misfire. The first time was due to a faulty spark plug wire about 5 years ago. The car has been well taken care of. All Plugs and wires are AC Delco. 99 % of the parts I use are genuine AC Delco. What kind of further perturbs me is if I call AC Delco about the Injectors for some Technical questions they won't talk to me unless I pay extra for technical assistance. Their product and they won't even give you any extra assistance unless you pay extra. I don't mean to vent but how can you sell a product and not back it up with a little Tech assistance.

I appreciate the Blazer Forum even more for all I have learned from others.

Mark

 

AC Delco and the Delphi FJ10565 are the same part. Amazon and eBay usually have them available for under $200. The up graded injector assembly relocates the injectors to the intake ports and eliminates the poppet valves. it is plug and play, no reprogramming necessary.

 

Aren't the new ones Electronic (no movable parts) as compared to the old ones which have springs inside the poppets controlling the fuel dispersal. I am wondering why my Cylinder2 misfired last night and I am saying that it was the Injectors. This morning it was like it never happened. Thats what I am trying to figure out. They are suppose to be better(Upgrade).
And Yes for 3 days it felt that way. I am wondering if I got a bad spyder assembly. Especially
if it starts to be intermittent. No rhyme , no reason.


I am not a master mechanic. I just do a lot of research to understand my truck.

I copied the explanation below from a site that was explaining the differences between the 2 injector systems.
CSFI versus MPFI

In the CSFI system, injectors are located centrally in the upper intake manifold and send pressurized fuel into tubes that run into each cylinder. This central body and long, leg-like tubes gives the system an emblematic shape, leading many to refer to it as the "spider injector system." It is the tiny poppet valve assemblies at the end of the pressurized tubes that cause the most trouble within the system.

This poppet valve is controlled by a mechanical spring, making it is very sensitive to fluctuations in the fuel pressure. Not enough pressure and the valve won't open enough, while too high of a pressure will unintentionally keep the valve open too long, leaking fuel into the cylinder. The other issue is that the end of a poppet valve is positioned just above the intake valve to each cylinder. This puts the valve very close to the hottest part of the engine; the combustion chamber. After every spray, the poppet valve is coated with residual fuel. The latent heat of combustion bakes the fuel, creating minute amounts of varnish. With roughly a few million combustions occurring in each cylinder for every thousand miles driven, this fuel varnish can quickly build up enough to partially block or completely clog a poppet valve. The best way to solve these problems is to get rid of the poppet valve altogether.

There are several aftermarket companies that sell a direct replacement for the problematic CSFI system. The major difference between the two systems is that the aftermarket system removes the faulty poppet valves and replaces them with electronic injectors located at the end of each fuel tube. These new MFPI injectors have a much larger opening making it very difficult to clog an injector. In addition, the injector is now opened electronically instead of mechanically. This maximizes the performance of the engine's stock settings by precisely controlling them when fuel injection begins, as well as the duration of the fuel spray (pulse width). This will translate into a quick, crisp response during acceleration.

After reading the explanation of how an MFPI injector is doing its work I am wondering
why I had a Misfire that disappeared the next day. Computer/Electronics to Blame?

Thanks - Mark

 

The upgrade totally eliminates the mechanical poppet valves. The six injectors, instead of being located in the fuel metering block, are relocated to the intake port, (where the poppets used to be). It doesn't totally eliminate the "mechanical" aspect, as both styles of injectors are electro-mechanical. But it does eliminate one mechanical part, which is a plus in making it simple.

That's a pretty accurate explanation. What might help, is if you can post the freeze frame data when P0302 was set. It will show a "snapshot" of all sensor data when the misfire ocurred. That will tell if the misfire was caused by a lean condition, or a rich condition, which will point us in the right direction to diagnose what happened.

EDIT: During the upgrade, there are a couple of things that need extra special attention:

#1 One of the fuel injector lines comes very close to the rear of the plenum, if it gets pinched, you will certainly have a lean misfire.
#2 If the fuel metering block is not pulled up into the plenum fully, it will create a vacuum leak past the oval shaped O ring... causing a lean condition, and high idle