my 89 just started stalling out when decelarting to an idle, like coming to a red light, or stop sign. Especially with the A/C on. It will start right back up again no problem; but I noticed it is idling low. like at about 600 rpm.

4 months ago I replaced the entire "top end". injectors, IAC, EGR, cap-rotor, IAT. There are NO codes being thrown.

Could it be my $50 autozone IAC crapped out ??
It also has a hesitation when cold that I could never find, but once in closed loop, she runs (ran) fine.

 

I wonder if the IAC needs reset...

 

after 4 months of running perfect, what would cause it to be "unset"?

 

Sounds familiar! One simple/cheap thing to check early on is the FP RELAY. If it is similar to my 86, the relay just gets old/corroded, and starts exhibiting these types of symptoms out of the blue! Oh, and at least on my 86 - no codes!

 

Also coolant temp sender could be bad. The ECM needs to know proper coolant temp to control fuel delivery, idle speed, spark timing.

 

ok, I took my used (but good) IAT sensor, and installed it as my coolant temp sensor. We'll see what happens.

It was stalling intermittently when hot, but that fixed itself. No explanation. No codes. just stopped happening.

Open loop still has major problems, runs terrible, bucking, hesitating, stumbling. But once it hits operating temp, she runs fine.
I can't figure this one out.

 

Unplug MAF sensor. Just fixed mine. 89 vert. No codes stalling. Unplugged MAF and worked fine. Then bought new MAF sensor. All is good now. Runs on MAF during open loop.

 

my 87 was stalling at the lights and would start back up, turned out to be the O2 sensor!

Just a thought

Rob

 

Unplugged the MAF sensor, car ran worse, way worse. The CEL came on immediately, but it didn't run any better.

This TPI is too Finicky when cold. Low RPM's stumbling, hesitating, etc.
Once I get the RPM's up, it gets past the problem.

What sensors control the car when cold (Open loop) ??

I might spring for a new TB...

 

As I replied to your post earlier, you seem to have exactly the same symptoms as I had with my 86! Despite what others(and the FSM) said, or implied, the fault WAS a bad F.P. Relay! Since the relay is relatively cheap, I urge you to relace it, or at the very least thoroughly test the old one. Have you done this? Cheers!

 

Where can I get a fuel pump relay?
I can't find it at rockauto.com or napaonline.com
is it named something else ?

At this point I have no hesitations about replacing parts. Especially since everything is ~20 years old.

 

I dug out the old invoice from my Chev Dealer on the new F.P. Relay - it says it is/was #14078915(GM#?). Came in an ACDelco box - box label also said - Relay #212-307. Now this was for my 86 - I do not know for sure if your 89 uses the same Relay? Completely solved my problems, at least. Cost was approx $20.

 

Damn Dude, you sure you're using that thing right?

 

I was looking under FUEL !!

 

Relays rarely cause intermittent problems - bad connections do and though replacing a relay might lead to a cure, it's only because you've re-established the connection.

Instead of throwing money at parts, buy yourself a scanner and that will give you the clues you need to fix it. Fuel delivery, as previously mentioned, is controlled by the Coolant Temp Sensor Signal. Essentially, it takes the place of a Choke. All you've verified is that the Sensor is ok. You don't know if there's a wiring problem or the ECM could be bad and the only way to see what the ECM is seeing is with a scanner.

A few of us, including myself, had the ECM toggling this signal between 225 and 250 degrees, even when the motor was cold, so our Vettes didn't start or drive very well until the engine warmed up. The sensor was fine, the ECM wasn't. But I can't say that your Vette has that condition, because I've also experienced the loss of the a/c signal, which can lead to the driveability issues you've described. And there are other causes, which without some data, we can guess at and help you increase your supply of spare parts - or you can find out what's really going on and give yourself a much better shot of actually getting it fixed and your Vette back on the road.

 

Assuming you have performed the 'tape the fuel pressure guage to the windshield' test and all was well, I would suggest testing your pick up coil. They're ~ $40 at Orielly and can cause intermittent spark issues.

Also, 20 year old relays are suspect. Throw a hunnerd at replacing as many of them as you can. MAF, MAF Burnoff, Fuel Pressure, etc. Clean the connectors while you're there!

 

I really can't imagine it being the FP relay, since that would affect it hot and cold, but for $15 who cares. I have no problem throwing parts at the car. especially cheap parts that are 20 years old.

But $400 for a MAF is out of the question.
The new TB is on order, and well as some other cheap parts.
we shall see if I can get my friends $500 scanner next weekend.
Either way it's a PITA because I have to wait until the motor cools off.

 

I have what sounds like the same problem on my 85. Rough idling, stalling out at lights and runs great while cruising. What exactly is the F. P. relay?

 

Fuel Pump Relay, on my 86 it's mounted to the firewall behind the Throttle Body