'95 Sierra - hesitates when cold...

[Steves95Sierra]

When 4 to 6 hours cold.., my '95 Sierra hesitates terribly when accelerating off the line - almost stalls completely at times. But when warm, I have no problems - almost as if she wants to run lean all the time, regardless of engine temp...

 

She's a C1500, 305ci w/2-point TBI (H motor) & 78K easy miles.

 

This is what I've done so far....

Replaced inline fuel filter

Checked for water/crap in the fuel tank

Checked fuel pump / fuel pressure

Replaced O2 sensor

Replaced distributor cap & rotor

Replaced plugs & wires

Tested TPS

Cleaned throttle body & replaced ALL seals & gaskets - including injector seals, filter screens and pressure regulator diaphragm

 

No OBDI codes are returned...

 

What's next... Any ideas???

 

Thanks for your help.

[Steves95Sierra]

btt - begging for help...

 

Two things that MAY be related, but I haven't tried...

 

Haven't replaced the CTS - coolant temp seems to show correctly on the console.

Haven't replaced the MAP sensor - I would think that if this is the culprit, I would have the problem whether hot or cold...

 

Just happens when it's cold.

 

ECM Problems???

[Steves95Sierra]

ok.., how about this...

 

An EGR valve stuck partially open? maybe?? anyone???

[getcrunk88]

does the engine stutter when it is idleing or just as soon as u hit the accelerator

[Steves95Sierra]

does the engine stutter when it is idleing or just as soon as u hit the accelerator

 

<{POST_SNAPBACK}>

 

 

 

Yes Sir (sorry if I assumed wrong) - slight shutter at idle.., then step on the gas and she drops out, nearly stalls before coming off the line.

 

If I disconnect and plug the EGR vacuum line to the solenoid, she runs much better, though a slight hesitation still exists. I'll also (with EGR disconnected) get a DTC32 (EGR Sys) after highway driving, which would lead me to believe that the solenoid is ok 'cause it's sensing no draw from the valve - I think.

 

Just wondering if the valve bellows is stuck open, has a leak, or the return spring has weakened over the years...

[getcrunk88]

Just a guess but have you tried the iac valve could be dirty or stuck closed, or could just be plain worn out. Just a guess

But the egr valve just might be the problem i would get an aftermarket egr valve and throw that on there. They arent too expensive running around 30-50 bucks it could save you alot of headaches in the future and also narrow down the problems.

[Steves95Sierra]

ahh.., the IAC valve. Good idea! I cleaned and replaced seals on everything in, on and around that dawg-gone throttle body but that.

 

I did pull the EGR valve off the manifold last night and it had some carbon build up around the plunger - but nothing unusual for an 11-year old truck with 78k. One thing I did notice.., the bellows was slow to return after pressing it up into the EGR body. Like you suggest.., I'll go ahead and replace it tonight and pull the IAC to take a look.

 

Thanks for your help 'getcrank88'

[getcrunk88]

No problem man i hope its the iac valve good luck!

[ChevyTech007]

If that does not take care of it, you might want to check the exhaust back pressure. I have seen a slightly stopped up exhaust cause to much exhaust to enter the intake when the EGR opens causing a hesitation.