The ECM is old and crude. It will trigger a code if the sensor is way off or missing. Don't rely on the codes alone. O2 I can see. Injectors, sure. Why MAP?

 

It idles (and runs) like sh*@, when it goes to closed loop it just about dies, then surges, then almost dies etc... I've read that some idle issues are MAP related. It doesn't cost that much so I figured what the hell just replace it anyway. I full throttle body cleaning and rebuild (gaskets) will be next weekend. I'll track down the problem(s) one step at a time. And yes injectors will be replaced as well.

 

It could be MAP related but it is best not to change parts since we don't know if the new part is good or bad. Don't introduce variables. Do it step by step unless it is a maintenance item. Get yourself a FSM if you don't have one and a scanner. NOT a code reader, a SCANNER that will give you live data.

What I would do at this time is to change plugs and wires and cap and rotor if they are old. For wires, I would run the car in a dark garage and spray a fine mist of water AROUND the wires and if there are any sparks, they need to go.

Take the TB off. This is a good time to do the coolant bypass. Take the top plate off, take the IAC off, take the IAC housing off too. Clean all passages. DO NOT SCREW WITH THE IAC. Just spray the pintle and wipe GENTLY. Reassemble with new gaskets.

 

I do have the FSM "Electrical Diagnosis Supplement", it came with the car. As far as Scanner is concerned I think I might pick one of those up this weekend. Superb advice to a Corvette newbie (I'm actually a pretty good mechanic, but I've only worked on 60's and 70's vintage cars...these electronics are foreign to me).


Also, and recommendations on a good scanner?

 

Don't really care what you are used to but either way, it is about getting fuel to the cylinders so that is the concept you need to accept. The way is just more controlled. Instead of your jets and air pressure, you have injectors. To control the idle speed you have the IAC which is a metered air leak. Timing still has to be advanced and this is electronic. Principles are still "Suck, Squeeze, Bang, Blow".

SnapOn MT2500 or Tech1? Both older and cheaper but work well?

 

Thanks again man, I'm looking forward to this new experience...based on the concepts I know so well. Glad to have fellow travelers like you and others in this forum to help guide. You've changed my mind on my first move with this...SCANNER. I'll keep you updated!

 

To clarify...I need an OBD 1 scanner, not OBD 2. Correct?

 

Yes

 

Im thinking of buying a 12 pin OBD1 / USB adapter for my laptop...then downloading TunerPro.

 

That works but you have to have a bulky laptop.

 

Update Bump!!


I've been pretty busy with work (got to pay for parts somehow) so I haven't done too much to the car.


So far I've replaced spark plugs (fu$@ you cylinder #2), cap and rotor and it's already made a huge difference, it runs soooo much smoother, I think the cap and rotor were factory original (81,000 miles). I was going to replace the plug wires but they are in great shape, so I'll leave alone for now.


I've ordered a TB rebuild kit and a new IAC valve, this work will happen this weekend. I've also bought a new O2 sensor and will replace that as well.


I bought the car from the second owner, he lost one set of keys, so I checked the resistance of my VAT key (#2) and ordered a new one, will have that cut when it's delivered next week.


I also purchased a 12 point - USB plug (OBD 1) to run a diagnostic on my laptop, and will be using the TunerPro program with that. This will probably happen in a few weeks...I'll make sure to take a pic of the operating parameters and post for all to see.


It runs great in open loop, (so much better with the new plugs/cap/rotor) then dogs out in closed with a fluctuating idle...so I'm hoping the new O2 and IAC will solve that...I also have my eye on the MAP, but I'll wait for my diagnostic program analysis before I make the decision to replace that. I'm also researching how to check for vacuum leaks as well.


That's about it for now...I'll report back when the O2 and TB have been replaced/cleaned.


Thanks for all the help!

 

How did you determine this? Have you checked for spark leakage or just "it looks good from here"? One way is more reliable the other is guesswork.

What exactly is in this "rebuild kit"? Is there something wrong with the TB? Have you tried cleaning first before doing the bushings and all that?O2 sensor, fair enough. Probably old.

Very simple. After the TB is cleaned, get the engine hot and at stable operating temperature and shut everything but the engine off. Scan it and try set the base idle. It should be around 20 to 30 counts. If you have more counts, the ECM is increasing the "metered air leak" because it needs more air. In which case, you turn the idle adjustment screw in, rev and recheck. If it is less, you turn the screw out, rev and recheck. If you have turned it all the way out and it still says 0, you probably have an air leak somewhere. This is because the ECM is trying to close off the "metered air leak" because it has too much air. If the TB is shut close and the IAC is set to 0 by the ECM, it is trying to reduce air and probably means that air is going in somewhere, hence the leak.

 

Actually I followed the advice of a post I read on this forum (always believe the internet lol), first inspected each wire visually for flat spots or other breaks, then with lights out took a spray bottle set on a very fine mist and sprayed over wires to see if I could spot any arching from the wires. Both methods yielded no flaws.


[/QUOTE]
What exactly is in this "rebuild kit"? Is there something wrong with the TB? Have you tried cleaning first before doing the bushings and all that?O2 sensor, fair enough. Probably old.[/QUOTE]


Rebuild kit lol, I need to get with the program...I ordered a "gasket kit" to reinstall after I thoroughly clean the TB...nothing will be rebuilt...hopefully.


Thanks for keeping me alert with terms aklim, it's the tough love from fellow travelers that'll get me through this. I'm having a blast by the way...this car has turned more heads in the few weeks that I've owned it than any other car I've ever had (and I've had some pretty cool old cars...check this out: )

 

Then save your money. Don't buy those wires that promise you "up to 5 HP" gain. At your level, IT WON'T unless the wires are broke.

I don't know. IF the shaft wobbles around, either rebuild or buy new. If not, a gasket kit comprising of the top cover, IAC housing to TB and TB to manifold. I have an aftermarket one so IDK if you have a gasket from the adapter to the TB but I don't think so.

I was assuming you don't have unlimited funds so I'm trying to make sure you don't simply go hog wild and buy everything in sight. There are a lot of people willing to sell you anything in their inventory.

So why did you think the IAC was bad? Hopefully you can make sure. You know the rules. Electric parts are non-returnable especially if they have been installed.

 

Nice Car! Great Colors

 

Regarding the hole in the center console; My '90 also has it and I found it to fit my garage door opener perfectly.

Enjoy your ride, it's spring.

 

I'll fill it with Skittles

 

I changed my old school mirror with the flip switch. Now it is electronic, has compass bearing (not that I use it) AND it allows me to program 3 rolling code openers. No more box on the shade or clunky stuff rolling around. Best of all, it dims electronically.

 

Can you point me in the right direction for a "flip switch"? Thanks in advance.

 

There is that flip thingy in the mirror. IIRC it is for bright lights in the rear.

I have a Gentex self dimming unit with Homelink