Uhh.... had one of those moments, any ideas?
Came home early this afternoon and picked up the Vette for a few errands. I had driven about 2 miles, the car was running fine. I stopped and went inside the school to pick up my youngest boy at day-care. I was gone about about 5 minutes and when I returned, the car had issues.
Upon trying to start it, it didn't immediately fire. I actually had to crank it a second (and maybe even third time). When it did fire, the idle ran high... maybe 16-1800 rpm? Then when I blipped the throttle to check for correct response.... blah.... nothing. It just fell flat and then immediately returned to high idle.
I was filling up the shorts because I had just left my little ones school and we are giving him a push in the potty training department.... AND I had just got the report that he hadn't dropped his 'deuce of the day.' So guess who's riding shot gun in daddy's vette with only his underwear on? Guess who doesn't have a diaper bag and the school just locked up? Guess who's wife is out of town and has no back up? You get the picture. I'm thinking... Man, just let me get home.
So I try to back up and the car hiccups and dies... absolutely flat on it's face dead. I had crept out of the parking space, so I just let it roll back to the rows behind me. I closed my eyes, took a deep breathe and just relaxed.

Anyway, long story short, I try it again after a minute of scratching. It fires after a moment, runs rough and settles out. That's it. No codes, no check engine, nada... zilch... squat. I was planning on taking this thing on a road trip (few thousand miles) on Thursday morning.

What's up with the Ghost of Vettes Past? Any good theories or like experiences???

92 Vert, Stock. 90K miles. In great shape mechanically

 

I think I would change the ICM depending on age and if stock or aftermarket maybe the coil as well it is never a bad idea to do them together. Whatever was acting up was affecting more than one cylinder and if no codes it probably was not a sensor it would have to be something the ECM can not check easily only 2 things come to mind ICM or coil or igntion secondary voltage or fuel injectors. When is the last time it had a real tune up?

 

Check the vacuum line on the fuel pressure regulator to see if there's fuel in it.

If there is a pinhole leak in the fuel pressure regulator diaphragm it will feed fuel into the plenum through the vacuum line. The ECM will compensate for the extra fuel by increasing the air into the plenum with the IAC valve, thus giving you high idle.

A bad O2 sensor can do this also. If the ECM thinks the mixture is too rich it will add air to compensate and increase the idle.

 

with these advices,may be a bad map sensor too, sounds like a vacuum issue.LESSON nex time use ONLY your daily driver for family activities...

 

Try a spray clean of the throttle body, maf sensor and air/idle and check the air cleaner/filter. Check the tps, ohm & voltage. Sounds like an air/idle valve problem. Check for leeking injectors also, maybe it flooded.

 

And...

blue absorbing pads, training pants, etc. in a bag in the back of the vette.

 

"A bad O2 sensor can do this also. If the ECM thinks the mixture is too rich it will add air to compensate and increase the idle. "

Won"t that usually throw a code (check engine light)?


I'm thinking O2 it's a possibility...car just squeeked past smog about a month ago just before I bought it. I've think I've noticed some off idle hesitation a couple times.

Okay, so on agenda: Full tune up and O2 sensor. I've never done it as this is the first C4 experience for me. Do you recommend screwing with it myself, or leave it to the people who do it for a living? I'm finding myself with less time and space for mechanical fixes (four kids)and I peeked at changing the the spark plugs.... is it as hard as it looks.

 

Then ICM and coil and inspecting vacuum lines.

 

You may have developed a leaky injector and it allowed fuel to drizzle....but this would only affect one cylinder on your car

 

Yes, the plugs are as much "fun" as you imagine, especially the right hand side...

 

Driving 2 miles then shutting it off = a restart that may be overly rich.

If it happens again after a short drive restart with the throttle depressed to the floor. This is "clear flood mode" & it should start & run properly.

Suggest removing the right side middle & rear inner splash guards for easy access to the spark plugs. Takes 5 minutes to remove them, the plugs can then be accessed easily with a long extension & swivel plug socket.

 

I wouldn't take the car on the trip....rent a car....

 

When I bought mine, the o2 sensor was bad. It sent out voltage in the right range, but was pretty much fixed at around 400-500. Which is about where it should be, so the computer never noticed to throw a code. I only learned by looking at a datalog.

I dont know about an lt1, but on an l98 you can change the sensor in under five minutes. It took me longer to set up the jack and to figure out which size wrench I needed than to do the actual work. $20 part, five minutes, no idea why none of the previous owners bothered to do it.

 

Although the symptoms seem that they could be related to the FPR or a ICM, the high idle give me a bit of trouble with those two items. I would also look at the IAC motor. If it is stuck or not moving correctly it could cause all those symptoms of hard start and high idle and can even make it quit.

Just replaced my FPR couple weeks ago that was a real bad leaker into the vacuum line. Caused hard starting and rough idle but no high idle. This was the second time for me replacing the FPR and problems were the same.

It's real hard to test the IAC and know it's defective. Sometimes lubrication will get it going and you can get by for a while but will not be a permanent fix. If it is bad, replacement is the only way. Sometimes replacement is necessary for finding the trouble also.