Hey guys,
i am new to this forum, and have checked out other posts/ threads related to the issue i am having, but i have one specific issue that i did not see listed here.
The basics: i have a 1993 blazer S-10 with a 4.3 liter W engine.
We do not use the truck frequently- maybe 10-20 miles per week.
Recent issue - we had a tough winter here in New York City and this seems to have had an effect on this truck. The battery could not take the cold and also the infrequent starting that it would take to keep a charge, so i replaced the battery. I went to start the truck- no go. if i hold the throttle body valve open slightly, it will start. if i close the valve, it will stall. Once it runs for a few minutes, it will idle,albeit roughly.
Ongoing issue- when i start the truck (cold) it runs rough and shakes badly. it stumbles for a few minutes than will steady out. not smooth, but enough that it does not stall. also upon start up there is a lot of fuel rich smoke from the exhaust. this goes away after a few minutes, but it does leave a stain on the driveway
it revs fine, and there is no loss of power doing highway speeds, so i tend to rule out a fuel issue.
my one specific issue is as follows: if i disconnect the black hose from the passenger side PCV valve,( the other end goes to the top of the throttle body, or IAC valve) the engine runs as smooth as new, no stumble or rough idle. If I put the hose back onto the PCV valve, the rough idle returns. The vacuum in this hose is strong (did not have access to my vacuum tester)
I traced the vacuum line to the top of the throttle body, and to the IAC valve.
I am not sure what is happening here.
I have vacuum and fuel testers,timing light, RPG gauge ( analog) also a digital multimeter ( i do HVAC for a living with car repair as a hobby) so i understand how the IAC and TPS reference voltages work. I am asking for advise on where to start looking. i plan on taking fuel pressure readings; what else should i look for? please point me in the right direction

Thank you in advance
Mikeymoe

 

How far have you checked into the IAC? That would be one of my first places to look if your problem is mainly during cold start.

 

Thanks for the reply Burning Soul-
i have not checked anything yet. i believe it is the IAC Valve that is causing these issues.
how do i check the IAC on this engine?
wy would the idle smooth out if the PCV is disconnected from the hose leading to the throttle body? would that bypass the IAC?

Just askin'....

 

A vacuum leak could cause the symptoms you describe as well. The PCV valve, if stuck open, would be a fairly large vacuum leak. Since the PCV valve is relatively inexpensive and you have seen that it can have an affect on the idle quality, you might want to start there. If a replacement doesn't help the condition, continue looking for a vacuum leak.

If you have checked over all of the vacuum lines and still have the problem, I would take a look at and clean the EGR valve next. If for nothing other than routine maintenance.

 

Thanks for the responses thus far. i plan on checking for vacuum leaks this weekend when i have more time to explore.
An update-
i pulled the IAC out, and noise aside, the pintle did extend fully. i cleaned the schmutz off of it and re installed it. if i disconnect the electrical connection on the IAC, teh idle shoots up ( and will set a code, 36 i believe).
this vehicle has an electronic EGR valve. what should i expect to happen if i disconnect the electrical connection with the engine running, should the engine die, or will it still run rough?
i plan on removing the valve and cleaning it, i just am not sure on how to properly determine if this valve or the IAC valve is bad.
BTW i did replace the PCV Valve- idle still rough when cold. with PCV valve removed from the vehicle, the engine runs smooth.....

 

I would deffinately clean your EGR Valve....I just replaced mine because cleaning was not an option as the pintle was collapsed. I was having some of the same problems you're describing and it helped mine.

 

Update #2
i was not able to get under the hood this past weekend, but i did order the EGR gasket. I plan on removing the EGR valve and checkingits function. Once i have that done, i will update again.

 

I was finally able to spend some quality time under the hood to figure out what is going on.
i checked out the linear( electronic) egr valve using tips from this website-
http://easyautodiagnostics.com/gm_eg...gr_valve_1.php
i had taken 18 Gauge 5 conductor thermostat wire, stripped the ends, and slid the exposed ends into the connector, of course keepig track of the color of the wire and A, B, C, etc. in the link above. i stripped the other end of the wires and used these wires for the readings. It helps to check for continuity between the conector in the plug and the other end of the thermostat wire to ensure you are getting a correct reading.
i performed these tests with the valve in the car, and one test with the valve out of the car. the valve passed these tests.
i didi clean the pintle seat inside of the valve, and also the passages in the lower intake manifold, and reinstalled same with a new gasket. MUCH chaeaper than replacing the valve.
i did check for a vacuum leak- no leak evident.
i also checked the fuel pressure- this gets interesting-
KOEO the fuel pressure was approximately 60 PSI. engine running, i read 55 PSI. i let the engine run for a while, and back to the engine off ( key out of the ignition) the fuel pressure went to 60 PSI not quite a leak down, so i know the regulator seems to be working.
the bottom line is the truck does run smoother (so far) when its cold, which is what i was looking for.
i also found out that the truck is not used much so i might have had carbon build up on the EGR and IAC valves ( which i had cleaned and re-installed), and a non faulty PCV valve ( which was changed).
Next stop is check fuel system.......

 

This would indicate to me, as you stated - a rich condition - not a lean condition that a vacumm leak would create. Pumping the accelerator pedal prior to starting, an improperly adjusted choke, sticking throttle valve or linkage, etc. could all cause this condition. Since the vehicle sits more often than being driven I would look for these problems before component failure.

 

thank you for the confirmation.
the accelerator does stick on occasion- i did not want to change poarts at random until i nailed the problem.
next up is the fuel system......