My buddy's TPI(my old engine) is having problems idling. It idles ok when you start it up and the engine is cold. BUT, after it warms up and goes into closed loop, the idle is really shaky. Sometimes when you take off from a dead stop, there will be like a "dead spot" in the throttle. Ill put into a list of what we've checked. Please help......the engine didnt do this in my car....


Replaced spark plugs(champion)
Checked wires for resistance
Checked cap/rotor(both ok)
Replaced 02 sensor(Bosch)
Replaced all vacuum lines
Cleaned IAC passages in TB and cleaned IAC valve(no TB cleaner used by motor)
Adj TPS sensor and checked for dead spots in voltage...read over 4volts at WOT
Cleaned EGR valve and passages
Replaced PCV valve and checked for blockages
Replaced coolant temp sensor


Thats everything we have checked or replaced so far. I havent checked the fuel pump or filter.....but if those were bad wouldnt they do it ALL the time, not just when the motor warms up?? I also havent checked the timing for the same reasons. Im also suspecting the Purge Valve on the fuel vapor canister but wanted to get some opinions before replacing anything else. Other than a bad idle, the car drives fine.....doesnt seem to be low on power and will rev all the way to redline. Suggestions? Thoughts? Comments??? help.......

 

Anybody??? Vader?

 

is it throwing any error codes. the tps could be bad. the cat could be clogged. the plugs could be bad.

 

No there are no codes. I checked the TPS three times and even swapped it with a known good part...still the same. The plugs have about 500miles on them...and all look good and are gapped correctly. The converters are BRAND new....havent even been out on the road yet....and there are no exhaust leaks. I tried capping off the place on the TB where the fuel purge line plugs onto the TB to see if the purge valve might be stuck open....but no luck there either. We did notice when we took off the TB the last time there was oil on the front of the gasket.....inbetween it and the TB....just wondering if that might cause a vacuum leak if the TB gasket isnt sealing all the way......?????

 

i would check that stuff anyways. sometimes you just can't assume when it comes to cars. and they're easy checks.

 

Very true....just a bad assumption. We are going to hook up a fuel press gauge to it in the morning and go drive around to see if there are any variations in FP. Im also gonna go ahead and check the timing to see if maybe the chain stretching when it warms up or something freaky like that........We went ahead and changed the filter tonite....seems to smoothed out some, but the idle is still bad. Isnt there a test you can use for the pump to see if its putting out sufficent flow??? I read it somewhere but dont remember exactly what you do. I think you disconnect the feed line at the intake manifold and hook up a piece of hose to it and ground the pump on the aldl....and if it pumps so much in a certain time, its ok....sound familiar?????

 

After you check the timing, you may want to check the resistence on the fuel injectors. A few years ago, my car idled terribly... it surged and shook alot.

After replacing all kinds of expensive things, I checked the IAC sensor and found it was full of carbon. I then checked the resistence on each fuel injector and found that 5 out of 8 were out of spec! After replacing the injectors & IAC, the car idled great.

Hope this helps.

 

After you check the timing, you may want to check the resistence on the fuel injectors. A few years ago, my car idled terribly... it surged and shook alot.

After replacing all kinds of expensive things, I checked the IAC sensor and found it was full of carbon. I then checked the resistence on each fuel injector and found that 5 out of 8 were out of spec! After replacing the injectors & IAC, the car idled great.

Hope this helps.

 

What is the resistance supposed to be for each injector??? I will check that tonite when I get home.....

 

I believe they should each be around 11 ohms. Unfortunantely, I am at work now and do not have my trusty Haynes manual to get the exact range. I can post the resistance range, but not until tomorrow morning (don't have internet access at home).

 

KYL98,

Fuel Injector Resistance (TPI) is 11.0 to 14.0 ohms, according to my Haynes manual. Sorry this is late.

Good luck.

 

Kyl, do you have a scan tool or laptop to see what the car is doing?

 

How exactly do you check the injectors? Do you just pull them out? Ignition must be on right? 11-14 seems like a large range though. Thanks

 

I just checked mine with the ignition off...you just unplug the injector from the harness and then check for resistance with a good multimeter. All of my injectors were around 13ohms, so I guess they are fine. Im taking my car to a known Camaro/GM mechanic that comes highly recommended to hook up to his diagnostic computer......Ive been driving the car hoping to get a code....but no luck and Im running out of patience..lol

 

Had the same problem with my 88 LO3. It started messin up once in a while, then more freqently untill it became allmost un-driveable! CHECK fuel pressure! I cleaned and replaced everything you did. Turns out it was only priming at 5lbs and idling at 7 1/2 lbs. The pump didn't just give it up, it just slowly kept getting worse. I'm changing my pump this week-end.

 

Why in the hell did GM put our pump in the fuel tank? It seems to me they did this kind of stuff to our cars just to be a-holes.

 

Well turns out it was a couple things making one big problem....the vacuum line going to the FPR was shot....causing variations in vacuum at idle. Also, two injectors were leaking down after shutting engine off. The varations in vacuum were causing a lean exhaust which got worse as the engine warmed or went into closed loop. Plus the fuel filter was clogged......Runs like a champ now.

 

Good deal man! It's hard sometimes to diagnose your own problems because of the freak factor. (My car ain't running. My car ain't running) know what I mean?

Irocstr, They put those pumps in the tanks to support the local dealership mechanic's. BIG $$$s for them!

 

Yeah, that's what I thought. There is just too much stuff on these cars that can be causing my bad idle/bad mpg. It just sucks. Gonna fill her up soon and get a new mpg, so I can see if what I did last week helped any.

 

Guess you missed one, eh?

 

Yep..lol That one never crossed my mind. Oh well.....thats how you learn right?