My 91 Z28 has been acting funny lately....It was running ok the other day until I put new exhaust on it. Now I dont know if thats the cause(Im going to see if I knocked any connections to knock sensors, etc loose) or if it just happened in conjunction with putting it on. Heres a rundown of what Ive checked....

Spark plugs(replaced today)
Wires(checked ok...all had "about" 14Kohm resistance)
Coil(checked ok)

Adjusted TPS and cleaned IAC
Replaced 02 sensor

The car idles ok until it goes into closed loop....then it starts running almost like it has a dead miss to it. I also put some fuel injector cleaner in....and gave the vacuum lines a once over(most have been replaced recently). I have ruled out fuel problems and vacuum leaks because wouldnt it idle like crap ALL the time if it was one of those??? Im stuck, cant figure this out. I might go ahead and replace the wires(about a year old/Accel 8.8) and see if its a wire "breaking" down. What else am I missing here? EGR??? I dont have any trouble codes....is there a way to check the EGR without taking the upper plenum off?? I have disconnected the battery a few times...to erase what the ECM had learned...but no luck there either. Need some help TPI gurus....thanks:hail:

 

explain funny? is it spuddering, knocking, stalling?

 

mine actualyl started doing the same thing 2 weeks ago.. except mine threw a o2 lean code.. yet i know since i dotn have a new chip in.. im running HORRIBLY rich.. so i dont know what the hell is up

 

 

Well it seems to run fine until it goes into closed loop. Then it starts running like its misfiring at idle. It kind of cuts out when you take off from a stop....but if you get on it after its moving, it seems to be ok. Would the IAC cause that after its warmed up?? Or would it be the EGR??? Fuel and timing would be constant, no matter if its in closed loop or not, correct???

 

You mentioned that it started after the exhaust work? I would check that the O2 sensor lead hasn't melted onto an exhaust pipe. And check for exhaust leaks prior to and around the O2 sensor.

With it going closed loop & then having trouble points to an incorrect O2 reading.

RBob.

 

I thought the same thing, untill he said he replaced his... then I didnt think anything of it... maybe the lead is burnt... didnt think of that. Check it out. Close loop deff. sugest 02 failure.

 

Well...checked O2 sensor...looks fine..nothing melted. Just wondering if my EGR is stuck open....but then again it runs ok when cold....just starts acting up after the engine warms up .....Hmm...now what? Any way to check the O2 sensor with a meter to see if its defective?????

 

I just got done doing some troubleshooting. Last nite I took the TB off and cleaned everything....took the IAC valve off and gently rocked the Pintle back and forth till it came off and wiped everything cleaned and put some light oil on the shaft and put it back together. When I started the car this morning, it ran fine till it warmed up then started idling rough as hell again. So, I shut it off and adjusted for minimun air and checked the volt to the tps...all fixed and ready to go. Started it up again.....and it still idles rough....except now it "searches" for an idle....it goes from 600rpm to 900 and back and fourth...like Im revving it or something.....and it smells really rich. So now Im thinking the new O2 sensor is defective. I unplugged the connector to the O2 sensor and started the car(still warm). It idles EXACTLY the same as if the sensor was connected. So is it the sensor????? Also, I still dont have a complete exhaust on it yet, would that affect it?? Its complete back to the Hog-ring clamp where the cat-back would hook to.....just wondering if the difference in backpressure would affect the EGR's operation....or is the EGR just stuck open or closed?????? Help!!!! Im about ready to drive this thing over a cliff

 

u could try getting a new maf power relay and new maf burn off relay
that might make a difference.

 

That would probably not help considering its a Speed Density car...not a Mass Air car..lol. Im gonna rip apart the intake and try cleaning the EGR valve and see if that helps.....is there anyway to check the EGR solenoid??? I also checked the PCV system and valve as well as the EECS? system(charcoal canister).....that turned out ok.

 

I'm having similar problems with my TA after an engine swap. I never had these problems before and my EGR wasn't hooked up then. I had a vaccum leak from the port under the throttle body and it idled better than it does now. It will purr when you first start it up, but after a few minutes it starts to sound like my 79 camaro at idle. If you figure out what's causing it let me know.

 

Try the temperature sensor. The one in the intake manifold. Judging from the description you gave it might be it. I had similar problems.
Hope that helps.

 

Could a 180 thermostat cause it to do something like this? I was planning on doing the fan switch that is posted in the tech articles, but funds ran out.

 

I would try to get a complete exhaust hooked up. I had an exhaust leak between the collector on one of my headers and the y pipe and it caused the same exact problems for me. -John

 

Well.....I finally got it going. Checked EVERYTHING on the car, and found more wrong than not wrong...lol. The car had 4 leaking injectors, fuel pump that wouldnt hold pressure, a bad coolant temp sensor, bad EGR valve, and some bad vacuum lines. SO, while I had the motor tore apart I decided to replace the runners(SLP) and port the hell out of the plenum. I got a great deal on some ACCEL 24lb injectors so I went ahead and put them in along with a adj fuel press reg. Car runs GREAT now.....gonna play around with the ECM now that I have some software..lol. Thanks for all the help guys..