Greetings! I just (last night) purchase a 1988 z28 350tpi and it has some issues I would like to clear up right away. I am going to replace the IAC EGR maybe the TPS and the PROM. The problem is that when the car is cold started it will die unless I feather the gas for 2-3 minutes....after that it idles really rough until finally it evens out....then there's a little bit of hesitation....and if I hit the gas so as to rev the car from idle to 1500, there is a noticeable halt in rev then the car resumes revving. I think it's the PROM or the IAC...but since all the other parts are factory I thought I would replace them anyhow....any tips would be appreciated!!!

 

One thing that's good to do is check the computer for stored codes. https://www.thirdgen.org/newdesign/faq/thirdgen.shtml Second to last FAQ. That might give you an idea of what to look at.

You can test the TPS to see if it's working correctly and in need of replacement, and just cleaning the IAC may do you some good. If you probe one wire going to the TPS you should find it (if set correctly) to show around .54v with the throttle closed and move smoothly to 4v at WOT.

For the revving it might be possible that you have a dead cylinder. You can check the spark plugs and see if any are fouled and don't look to be firing, or check how quickly water evaporates off the headers to see if some tubes are not as hot as others. You could also listen and see that each fuel injector is firing, and that you've got spark at all cylinders.

Vacuum leaks also tend to cause a rough idle and stalling. It's quite easy to spray some propane or starting fluid around any place the intake may not be sealing well and see if the engine responds.

The EGR will not be causing stalling AFAIK unless it is stuck open. If you're going to replace it for emission purposes, you may as well check the injectors to see if they are leaking as well. It's possible to either pull them out and physically watch after priming the pump (turn the key and listen for it), or by clamping off the fuel return line and monitoring the fuel pressure. It should hold even without the return line clamped, but if it doesn't that may be an unrelated problem.

If you can successfully check for codes, the prom is probably still good. I'd only replace that if you've got an aftermarket one in there, since they're only $65 bucks or so from the dealer.

 

Injectors are good...pressure is good. I will have to check for stored codes like you said. All of the problems with the car disapear after five to six minutes after starting. Then it's perfectly fine. That's whats making me think that it might be the IAC.....I'm going to replace the prom anyway so I figured now would be the time before this becomes my primary driver. Also, have you seen a procedure for removing the plenum to gain access to the IAC?

 

The IAC doesn't change in 5 or 6 minutes. Nor does the TPS, the EGR, or the PROM.

There's exactly one thing that does:

COOLANT TEMPERATURE

Replace the CTS (coolant temp sensor) before you do any of that other "shotgun" stuff. I think you'll find that you just wasted a whole wheelbarrow fuill of $$$ on that other stuff, and that one cheeeep little thing is really the culprit.

 

sounds great!!! thanks

 

I changed the CTS this morning, car stalled the first time I started it, but after that it actually started to idle all on its own. No leaks, and yes I used teflon tape, and the car runs much better and there's no more of that billowing reeking of gasoline smoke out of the tailpipes. Once the car warms up the idle is still a bit rough, but that's nothing I can smooth out (I hope) Thanks for the tip RB83L69. I think the next thing on my list is to clear all the codes, then check for new ones...good idea??

 

YEP, sure is. I'd also consider doing a full tune up (plugs, possibly plug wires, and a distributor cap) since you have no idea when it was last done. An oil change might be a good idea as well. Just to make sure all the "normal maintenance" stuff is done so you can start with a clean slate....

 

The plugs and wires were changed one weekk before I got the car..the owner had all of the reciepts for all of the maintenance on the car for the last two years...the cap, rotor, and coil were also replaced. perhaps the 02 sensor??

 

Not a bad idea, especially if you don't know how old it is (or it's over a year old). Get one from a GM dealer if you do. The running real rich from the bad CTS could have messed it up as well...

 

I let the car sit for 1:40 minutes then re-started. The car cranked for maybe 3/4 of a second, then the car started and idled normally as if there were no problems whatsoever. Strange. I have a hook-up at a Chevy dealer, so that's will be a great place to look for the sensor, thanks for the tip! Now I just have to see if it will start tomorrow morning.

 

What's sp strange about that? Sounds pretty darn good to me.....

 

I'm just suspicious about how the car will perform on a full cold start. Hopefully it's going to be fine, but my instincts tell me otherwise. I am going to get the timing set, and make sure the gear is good, and what do you think about Valvoline Max life oil for the car, with Purolator Pure One filter?

 

Boy, now you're opening a can of worms!

First - the filter. My personal opinion is forget about it. I'd use either an AC-Delco or a NAPA/Wix brand. Or a Mobil 1 or Amsoil filter. Nothing else goes on my car. I used the AC until I got to 4K miles on the new motor then switched over to the Mobil 1 filter when I went to their full synthetic oil.

Oil - that one's probably fine. Depending on how many miles are on it, it's probably a good choice (especially if over 100K). Actually helped my old 305 motor not puff quite as big a blue smoke screen when you first start it up after sitting all night (which is a sign of bad valve seals). It's also what I use in my '95 F-150 with 275K miles on the clock.

As for your cold start-up, it sounded fine. I'd just see what it does for the next few days. I think the CTS solved your problems in that area.

 

I certainly hope so, let me see if I can get some pics...88 with 98k....many reciepts.....$1,800.00

 

Do I have to compress the pics???

 

gotta go to work....thanks!!

 

Ok....so I let the car sit all day while I was at work and started it as soon as I got home. It started more easily than it had in the past few days, however, it did need some help on the pedal once or twice, and it is running really rich, those nice puffy clouds of gasoline smoke were there, what could be causing it to run so rich? Any ideas?