Help! 92 Corvette - Random rough idle/severe hesitation on start and warm

[92AquaVette]

Ok.. I have searched, and can't find the exact problem I have.. so, please don't flame me if it is obvious, or been asked before.. I tried searching.

- So.. my 92 Corvette can be fine for a long while.. then, leave it sit (first happened after going to a car cruise about 20 mins from me) - and when I restart it.. bam.. rough idle (VERY) - and running like it's on 4 cylinders.. (rough, bogging, but not stalling..) - what I did this time, since it caught me off guard, was pull over.. pop the hood, look for anything obvious.. waited about 15 minutes, restarted it.. was fine the rest of the summer..

- Today - got the car out of garage storage (note.. had an issue where my battery regulator went out, and the battery went dead on me.. got a new one, no further issues..) - started it up, drove about a mile.. it was fine.. left it idle for a few minutes... still good.. drove about 5 miles, parked the car.. got something to eat.. came back out (about 30 mins later) - car ran rough on start (NOTE- car starts up fine, every time) - had no power again.. seemed like the same issue coming back, so I parked it.. left it sit for a few minutes.. started up again.. still there.. drove it for about 1-2 miles, hoping it would clear up.. nope.. pulled over again.. left it sit for a few minutes again.. started up.. it was FINE.. drove for about a mile.. and, yep.. started the same shit again.. so, I limped it home (about 3 miles) - put it in the garage.. and now.. here.. after an hour of searching for the problem..

HELP?
- Note: car was stored in the garage for the winter, battery did die, but it is holding charge fine, stored it with about 1/2 a tank of gas.. haven't put anymore in it yet.. didn't add any additives or anything to it before or after.. I'm dazed and confused... :confused;help

**UPDATE** - After going out and checking a few things.. and restarting the car, I noticed a VERY strong fuel smell, as well as some soft backfiring.. I'm leaning toward Fuel Injector issues at this point.. what do you all think? - Also.. could it be I need to run some fuel injector cleaner through the tank, as this gas sat in the car all winter? Please.. I really need some help here, my resources are limited.. Thanks in advance..

 

[92AquaVette]

Anyone??

I really need some educated input here.. please?

 

[hotmtrsports]

Enter "rough idle" in the advanced search and you'll get 20 pages of history.

......
Could be "could be"

bad fuel
water in fuel
bad injectors (especially if original) ... replace them all at the same time!
replace fuel filter

It would be a good idea to get a GM Service Manual as a reference.

Chuck M

 

[92AquaVette]

-

Enter "rough idle" in the advanced search and you'll get 20 pages of history.

......
Could be "could be"

bad fuel
water in fuel
bad injectors (especially if original) ... replace them all at the same time!
replace fuel filter

It would be a good idea to get a GM Service Manual as a reference.

Chuck M

Thanks..and,as I said.. lots of references to SIMILAR problems, but didn't find the exact problem.. which is why I asked.

Most of the "Rough idle" posts have one thing in common, that mine does not.. mine will start fine.. starts right up, in fact.. and sometimes it will be fine, other times.. awful.. that's the odd part of it..

The check engine light did come on for a brief time the last time I drove it.. so, I am going to check codes today.. I was kind of thinking the same things though, something to do with the fuel system..

- Checked the codes today, got the following:
1 - C12 (which I have learned means everything currently is ok)
4 - H13 - Which, from what I read, means Left Oxygen Sensor fault


Again, thank you for the input.

 

[DaveP85C4]

I am going to take a wild ass guess based on these symptoms. A: it will ALWAYS start. This tends to rule out optispark and fuel pressure issues. B: "Runs like it's on 4 cyls". Ie, very rough. The EGR valves on the LT1 are negative back pressure. If the valve doesn't seat after engine start, it will run very roughly. When it does it, open the hood and "gingerly" touch the EGR pipe leading to the rear of the intake manifold off the rear of the RH exhaust manifold. If it is hot, and getting hotter as the engine is running, the EGR valve is open. It should never be at idle.

Another hint: Some EGR valves have an exposed diaphragm. I don't recall if the LT1 does or not. If it does, with it running rough, push the diaphragm further open, and let it snap shut. Or just look at it to see if you can tell if it is open or not. If it is EGR, research 'Negative back pressure EGR valve". You'll find the common cause of EGR valve opening after start is blocked EGR passages. I haven't seen this to be a problem on the LT1 over the years on the forums, but who-knows? As I said, just a WAG based on the symptoms. Don't replace the EGR valve based on this post. The valve itself is almost NEVER the problem. Usually passages or vacuum hoses improperly connected.

Also check all 8 fuel injector's resistance. Pull the connector off and put your ohm meter across the terminals. Should be right around 18 Ohms each. If you find a few that are lower (12 or less) the injectors are bad and can cause the rough running, but usually it doesn't clear up or go away for months. Bad injectors usually cause rough running after warm-up every time until they are replaced.

There's a couple of hints.

 

[92AquaVette]

I am going to take a wild ass guess based on these symptoms. A: it will ALWAYS start. This tends to rule out optispark and fuel pressure issues. B: "Runs like it's on 4 cyls". Ie, very rough. The EGR valves on the LT1 are negative back pressure. If the valve doesn't seat after engine start, it will run very roughly. When it does it, open the hood and "gingerly" touch the EGR pipe leading to the rear of the intake manifold off the rear of the RH exhaust manifold. If it is hot, and getting hotter as the engine is running, the EGR valve is open. It should never be at idle.

Another hint: Some EGR valves have an exposed diaphragm. I don't recall if the LT1 does or not. If it does, with it running rough, push the diaphragm further open, and let it snap shut. Or just look at it to see if you can tell if it is open or not. If it is EGR, research 'Negative back pressure EGR valve". You'll find the common cause of EGR valve opening after start is blocked EGR passages. I haven't seen this to be a problem on the LT1 over the years on the forums, but who-knows? As I said, just a WAG based on the symptoms. Don't replace the EGR valve based on this post. The valve itself is almost NEVER the problem. Usually passages or vacuum hoses improperly connected.

Also check all 8 fuel injector's resistance. Pull the connector off and put your ohm meter across the terminals. Should be right around 18 Ohms each. If you find a few that are lower (12 or less) the injectors are bad and can cause the rough running, but usually it doesn't clear up or go away for months. Bad injectors usually cause rough running after warm-up every time until they are replaced.

There's a couple of hints.

I will definitely look into those, regardless.. but.. we replaced the Left 02 Sensor, and my gas mileage (which was only around average 10 yesterday driving from home to my father in laws) - jumped up to an average of 25 mpg.. so, I am guessing that, at the very least.. the 02 Sensor was definitely bad.. also.. no more running rich smell.. and the idle seemed much smoother.. didn't have it out too long (just missed a downpour.. lol) - but.. crossing fingers here that we found the culprit..

Again, thank you ALL for your input guys, you have no idea how greatful I am

 

[Rufusfruge]

Rough idle on occasion

Hi there,
Just to add my 2 cents as they say...you didn't mention if you had ever replaced the fuel filter or if you had drained the gas from the tank that had been sitting pull winter. I would recommend doing both and adding some sea foam to a fresh tank before taking it out for some weekend cruising. Don't forget a fresh air filter while you're at it. Enjoy the wave! Oleschl.