Hi all, my GF purchased an immaculate 88 Iroc convertible 6months ago and it has run and started as sweet as a nut till yesterday, when after having not been run for two weeks, she started it and backed it out and got to the corner and then it all turned to custard. Upon checking it over I find that it starts well but will not hold an idle and will miss badly and pop and fart up to 3000rpm and is fairly smooth by 4000. So I swapped out the plugs and checked for vacuum leaks, no change. My question is, where do I start looking now as it is not driveable,
Cheers Simon

 

Sounds like a TPS or IAC problem.
Clean the IAC and check the TPS voltage is smooth and reading right.
Then do the reset procedure just to be sure.
HTH

 

Thanks JP, I'll start with those two and let you know how I get on
Cheers Simon

 

Have had no luck with sorting this problem. Replaced IAC and reset etc, replaced TPS and tested idle voltage with smooth voltage increase across the range, tried another MAF I had and checked for vacuum leaks.Found one small broken vac pipe I replaced and blanked off vac hose to brake booster incase diaphragm was shot. None of the above has made the slightest bit of difference to the way it runs. I cannot keep it running unless its above 3000rpm and below that it backfires out the exhaust and back thru the plenum too and will die if I dont pump the the throttle and get it above 3000. No codes from ecm at all. Behaves like its a massive vacuum leak that I cant put my finger on. Now I,m getting grief because her car is not running and I'm not too sure where to look next, any ideas anyone? Would appreciate any help
Cheers Simon

 

I'd check the injectors and the fuel pressure regulator...Could just be running lean.

 

Hear is a statistic, 95% of the time it's fuel/Air and spark related the other 5%? Sensors.

 

i would ohm injectors first,then look into a possible bad fuel pump,ecm,or distributor related issue

 

test your fuel pressure first. ohm each injector. look for fuel in the vacuum line of the fuel pressure regulator. if you havent replaced the fuel filter in a while, that may be the problem as well.

 

How about a bad ignition control module?? I had one go and the car ran like someone was holding the brakes on and the temps went through the roof!

 

I had a bad prom once and it acted like this.

 

OK I'll get into the fuel side of things this weekend and see how I go. Its just so odd that it completely changed from running perfect to horrible like the flick of a switch.Thanks everyone I'll keep you posted on how I get on.

 

I had a similar issue with my old Z, turned out it was a combo of a non functioning EGR that was also leaking out the gasket...worth a look..

 

Yeah, I'm thinking a stuck open EGR could make it run like this, I think I'll get rid of it, no emission rules here, I'll see what I find this weekend, cheers

 

Careful, I did the same and my car would overheat if left at an idle for 3 minutes

 

Why would it overheat? My LB9 had the EGR Valve removed and now my 355 vortec does'nt have one either with no overheating issues.I like it that my engine breathes fuel and air only, not dirty exhaust sooting up all the inlet tract.When I strip my TB, plenum, runners and base off they are spotless inside.I would tend to think thats its better to have no exhaust gases heating up the base and the air being drawn through it must be cooler as well? Just my two cents!!

 

EGR only opens up at cruising speeds so that the engine can run a leaner A/F mixture without detonation, so it shouldn't be affecting your car in any way at idle

 

Check the #5 & 7 plug wires are not crosstalking or something else wire related.
Rich will pop out the exhaust, lean will pop on the intake. Odd that it does both leading me towards ignition problem.

if it were more popping out the exhaust I'd tend to look for a leaking injector flooding the plugs. Astock ignition will have trouble lighting them at lower rpms.

 

He is probably saying that cause , at idle is where a car will run the hottest. Your temp climbs at idle and goes down once you start driving.

 

Doesn't sound like an egr issue. Have you tested your fuel injectors? Very common to go bad on these cars.

 

I think it sounds like the water temp sensor that sits at the front of the intake that feeds info to the ECM,if defect it will tell the ECM its like well below freecing point and the car will run like **** and will not idle/splutter and if not reved really high it will cause you to restart the engine all the time.
Could barely take the car home when it happened to me,the fun thing is that you will not notice anything on the gauge watertemp as it does take the water temp from another sensor.
This problem happened like a lightning from clear skies from one second to the other.

Regards Mats

 

Well so far the injectors all ohmn out at 16.6 each which I think is perfectly normal. Checked plug leads for orientation and they all go to correct cylinders. Fuel pressure is normal 38-45 psi range.Still no further ahead on making it run better, just have eliminated a few things thats all. Gonna take a poke around the distributor now and see what I come up with. Thanks to all of you with your thoughts.

 

Just wondering how long it took you to determine this?
Cheers Simon

 

I got lucky,it was early in the morning heading for work when it happened stopped by the road pooking under the hood and a US pickup stopped and the guy was a owner of a speedshop/mechanic shop and he said it must be the ECM water temp sensor happened to his TPI Vette also some month ago and he was correct....sometimes you are lucky
Edit: I think you can ohm test the sensor i think its in the same harness as the TPS,it bottoms out at -40C degrees dont know what that is in Farenheit but somethimg like Polarfreezing....anyway the engine didnt like it at all.

Regards Mats

 

I had a similar problem on a carbed engine one time turned out something went bad in the distributor. This truck was my DD and I just started it up one morning and it didn't want to run, popping throught the intake and exhaust, I liked to have pulled my hair out trying to figure it out and just stabbing at things I dropped another distributor in and it was like magic it just fired right up.

 

Finally, having found the time to work on her, I have found two things that I think are contributing to the running issues of the car. I pulled the plenum off to check the EGR valve which was ok ( its gonna be blanked off) and found the throttle body gasket underneath absolutely shagged, gone hard and pieces missing, this explains the vacuum leak that the engine felt like it had, an easy fix! Then removed the dizzy cap to find the whole insides a ball of rust!!! It looks nasty so am gonna replace it with new as all the pickup arrangement is so corroded it falling to pieces!
Question- am I better off to purchase a stock GM dizzy as opposed to a $52-78
ebay item? They certainly look ok, are they worth a try?
Cheers Simon

 

A buddy of mine got one off eBay for his TBI truck and it works great. I believe he paid $55 for it. It's red and looks like an MSD.

 

on my 85 z28 tpi 305 i put an lt1 cam and lifters in it and it idles at 2,000 rpms but then goes back down, it does it for a while and then when i take it out of park it runs fine,

 

Am pleased to say the car is finally running and very nicely too with a $52 ebay dizzy which I couldnt fault as the stock GM cap fits it perfectly. New plenum and throttle body gaskets and blanked off EGR with no issues. Thanks to all who helped along the way with advice, much appreciated
Cheers Simon