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Rough Idling - May help someone else

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RonnieH

Well-known member
Joined
Sep 3, 2002
Messages
85
Location
Henrico, NC
Corvette
2012 Crystal Red Metallic
I had trouble for a couple of months with my Vette idling rough once it started to warm up. Let it cool back down, no problem until it got warm again. Seems I have seen quite a few posts with others experiencing same problem. It ran o.k. on the road, just idled terrible after warming up. After doing some initial troubleshooting and eliminating a couple of things, I felt sure it was the EGR valve. Took out the old EGR and sure enough it was sticking and full of carbon chunks. Put in a new one with extra gasket and screen as recommended by GM Junkie in previous posts. Problem persisted. I took it to a reputable shop in town. He checked it out for almost a day and told me he thought the engine was shot - he was seeing varying compression across a couple of cylinders after it warmed up. I had a hard time believing it - I only have 35,000 miles on the car and it has never been abused. Well, when I couldn't find anything else wrong, I priced out crate engines, etc. I didn't drive the car for a couple of months - too depressing the way it was running. As a last option and to get another opinion before replacing the engine or selling the car as is, I took it to a local Chevy dealer who has a mechanic that is great w/Corvettes. 5 of the 8 injectors were bad - 5-8 ohms on each one of them. I had checked the injectors myself about a year previous, and at that time all of them were in range of 14-16 ohms. Replaced all injectors with Bosch III's and it now runs like a dream.

Hopefully, this will help someone else troubleshoot similiar problem. My take away from the experience - don't overlook anything when troubleshooting and keep an open mind. Don't jump to the most obvious solution. Since I had checked the injectors about a year previous, it never crossed my mind they would fail so quickly. Could have been a couple of contributing factors - excessive ethanol in gas, not driving the vehicle (now that it runs so good, I appreciate it even more and am now driving it a couple of times a week vs. a couple of times/month previously) and just plain age.

In some small way, hope this helps someon else.
 
Sometimes it pays to re-check the obvious. I suggest all still with the Multex injectors plan on a quick replacement before the ethanol eats them up.
 
I drive to Florida a few times a year in a pickup and I notice everytime I'm down there the truck does not idle right. Yep...ethanol 10% used down there but I think it's more than that. As soon as I return it idles just fine. Fuel makes a difference. I guess the computer won't adjust to all that alcohol?
 
I had an 89 Buick Riviera that hated ethanol . Here in Iowa we still have a choice.In Minnesota they do not.

Glenn
:w
 
My 1989 runs fine with 10% ethanol (and that is with the stock injectors). I would remove and clean the throttle body and IAC, and check minimum air speed.
 
I had a hard starting issue on my 88 after warm-up. I have gone over everything on the car since I got it seven years ago. Checked out the injectors, they were all about 15.2 ohms. My injector problem was leak down, the fuel system would not hold pressure after 12 hours. I went with the Bosch GenIII injectors and the problem is solved, Sys. holds pressure, starts right up after warm-up, runs much better, I figure fuel mileage is better , but haven't checked it. I was a little leery on the injectors being 1/4 inch shorter, but there is no leakage at this point, installation was easy.
 
Leak down was the same issue I had on my 1988. Replacing the injectors solved that issue.
 
The coils of the injectors can vary and they usually do not effect idle quality. What CAN and DOES effect idle quality is the injector o-rings. They will get brittle and crack causing a vacuum leak. Sometimes once the engine is warm they might expand a little and seal up enough to smooth the idle some.

Changing the injectors means, of course, new o-rings which would take care of this vacuum leak.
 
Anybody know the most economical source for the Bosch III's?
 
muddywaters said:
I had a hard starting issue on my 88 after warm-up. I have gone over everything on the car since I got it seven years ago. Checked out the injectors, they were all about 15.2 ohms. My injector problem was leak down, the fuel system would not hold pressure after 12 hours. I went with the Bosch GenIII injectors and the problem is solved, Sys. holds pressure, starts right up after warm-up, runs much better, I figure fuel mileage is better , but haven't checked it. I was a little leery on the injectors being 1/4 inch shorter, but there is no leakage at this point, installation was easy.
Click to expand...

I am interested in this. Tell me what you think about this senario. My 88 runs fine. It idles between 6-8 hundred RPM, but doesn't seem rough. But I'd say 3/4 of the time when i go to start it, there is a problem. The best I can describe this problem is that I feel I need to pump the gas petal to get it to start (and I do pump the petal). Every once in a while when I turn the key the first time there is no engine noise at all, but I think that is an entirely different issue.

Thanks
 
I thought pumping the accelerator on a fuel injected car was a no-no? Again, my problem was after warm-up starting. When the engine was cold, it would kick right off, when it was warmed up, it would take what seemed like a longer period to start, then start slowly and come to an idle. When I removed the plenum it reeked of raw fuel and that was after I checked fuel pressure after 12 hrs., there was none. The Bosch GenIII injectors did the trick, now it kicks right off hot or cold. I also replaced the starter recently, I figure the constant extended start time did it in.........
 
Don't know if pumping a fuel injected car is a no-no or not. I have always done it to any car that was having trouble starting.

I thought this sounded similar to fuel pressue leakage, because it seems like the car needs to repump the fuel close to the engine after it has been sitting for a bit. But I am in no way an auto mechanic, and in fact most of what I know about cars has been learned from fixing this one.

My car does have a distince smell after I drive it a bit. I can only smell it from the outside, and I know I have smelled this smell somewhere before. I am thinking it smells like a tractor or a riding lawnmower, but kind of with a little more gasoline in the smell. For now, I think it is because I have a minor oil leak and I am probably cooking the oil that is coating the bottom of the car. My exhaust does not look unhealthy and the spark plugs looked normal when I replaced them.

How much does it cost to have someone inspect fuel injectors? It sounds like one of those things that is easy for a mechanic and difficult for the home garage.
 
MBDiagMan said:
Anybody know the most economical source for the Bosch III's?
Click to expand...

Check out the C4 section on the Corvette Forum. There is a vender there FIC, I believe, who sells the Bosch III's. I think he tests and flow matches them as well. I'd get them from him, lots of good reviews.
 
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