Help! 90 l98 corvette idles rough sometimes

[polobryan]

:confusedMy vette will idle rough sometimes, then other times runs great. When it idles rough, it also wants to stall out. I have to drive it a ways before it gets better. All the fuel injectors read 16 ohms. Any ideas?

 

[Schrade]

Welcome onto the boards there...

Good job ohming the injectors. Loping idle? Up and down, like a yo-yo? Pretty steady loping?

 

[vetteboy86]

Welcome to the CAC.

Is the "service engine soon light" illuminated?

 

[aklim]

All the fuel injectors read 16 ohms. Any ideas?

That only means that the injector solenoids are ok. It doesn't tell you what the spray pattern is so that test is not really good for much more. My car ran smooth and all that but one injector was flowing at 336 cc and the rest were at 412. SOTP dyno is absolutely worthless unless the situation is FUBAR.

Have you done a propane test for the leaking hoses? How is the spark? Have you checked the spark plug wires for leaks? How old are the plugs? Have you cleaned your TB and the passages properly? What about the IAC housing? Also is the IAC adjust right?

 

[polobryan]

help

It's a looping idle. Sometimes it does it then sometimes not. I pulled the IAC and cleaned it up. The service engine light is not on. I ran it today and its doing the same thing. But oddly enough the "sys" light is flashing in my cluster. I have heard this is a battery issue often. Spark plug wires are fairly new, I'm guessing the plugs were replaced the same time. Going to replace the plugs Friday just in case.

 

[aklim]

I pulled the IAC and cleaned it up.

But oddly enough the "sys" light is flashing in my cluster. I have heard this is a battery issue often.

Spark plug wires are fairly new, I'm guessing the plugs were replaced the same time. Going to replace the plugs Friday just in case.

Did you clean the TB passages? Did you take out the IAC AND the housing and clean that?

Maybe, maybe not. Read it first and see what it i. It could be your AC fuse that blew. When mine did, the "SYS" light came on.

Only one way to know. Run the car in the dark and spray a fine mist cloud to see if there are sparks. Also, how is the cap and rotor?

 

[Schrade]

It's a looping idle. Sometimes it does it then sometimes not. I pulled the IAC and cleaned it up. The service engine light is not on. I ran it today and its doing the same thing. But oddly enough the "sys" light is flashing in my cluster. I have heard this is a battery issue often. Spark plug wires are fairly new, I'm guessing the plugs were replaced the same time. Going to replace the plugs Friday just in case.

Could be a poorly seated IAC, or carbon-fouled IAC pintle.

Did you flip the IAC gasket? Or use a new one? If it's in good shape, a light film of grease will help seal, better than going on dry...

Battery problem could be the reason for the SYS light. Get your battery load-tested. Good result probably means good, but bad does NOT necessarily mean bad. I've had 2 test 'bad', one lasted an additional year, the other is still in.

 

[aklim]

Could be a poorly seated IAC, or carbon-fouled IAC pintle.

Did you flip the IAC gasket? Or use a new one? If it's in good shape, a light film of grease will help seal, better than going on dry...

Battery problem could be the reason for the SYS light. Get your battery load-tested. Good result probably means good, but bad does NOT necessarily mean bad. I've had 2 test 'bad', one lasted an additional year, the other is still in.

Or how about the passages being fouled and the IAC cannot close and open properly? Maybe even the passages in the TB are caked up. Won't know till you remove the TB and the IAC housing and clean it.

I wouldn't. I don't flip my condoms after use and I don't reuse O-rings or gaskets unless they are specifically made to be reused.

http://www.corvette-guru.com/uploads/smartsection/3_CCMCodePull.pdf

 

[Schrade]

Or how about the passages being fouled and the IAC cannot close and open properly? Maybe even the passages in the TB are caked up. Won't know till you remove the TB and the IAC housing and clean it.

I wouldn't. I don't flip my condoms after use and I don't reuse O-rings or gaskets unless they are specifically made to be reused.

http://www.corvette-guru.com/uploads/smartsection/3_CCMCodePull.pdf

No condom-flipping??? That's not very 'green'...

 

[polobryan]

help

I used a new gasket on the IAC. Replacing plugs tomorrow. Idling better since replacing battery. Alternator checks good. TB is clean, but can you clean behind the TB? Is that what is called the plenum? Will also check rotor tomorrow. Thanks for yalls help so far!otfl

 

[aklim]

I used a new gasket on the IAC. Replacing plugs tomorrow. Idling better since replacing battery. Alternator checks good. TB is clean, but can you clean behind the TB? Is that what is called the plenum? Will also check rotor tomorrow. Thanks for yalls help so far!otfl

Gasket? There are 2 gaskets. One where you screw the IAC in and the other when you take the IAC off. Take the TB and then the IAC housing off. Clean the pintle and the area around it from the inside. Flush the passages out with brake cleaner. If your plenum is clogged, you have other issues. Stop being lazy.

 

[Dukeallen]

No condom-flipping??? That's not very 'green'...

View attachment 1762

:LThat's the one thing that makes me nervous whenever I've bought a used car, and go to clean the back seat. I do NOT want to know what the PO did in it.
hnoes

 

[aklim]

:LThat's the one thing that makes me nervous whenever I've bought a used car, and go to clean the back seat. I do NOT want to know WHO or what the PO did in it.
hnoes

Corrected for you.