Help! Rough Idle--intermittent

[FForward]

I replaced the o2 sensor and checked the grounds recently and I still have the slight miss plus a little surge at times. I was wondering if the ESC has anything to do with it. It has never been replaced. I disconnected it while the car was running at idle and nothing happened. As it now stands the complete fuel system has been replaced from pump to injectors. The ignition has had all new plugs, wires, complete dist., and timing is set to TDC. The EGR was replaced and I checked for vacuum leaks with the propane method. It happens in both open and closed loops. The TPS seems to be operating ok and is set to specs. The IAC was cleaned along with the throttle body when the new injectors were installed. The MAF, IAC, ESC, and TPS are the orignals. Because I have the Bosch Gen III injectors it was suggested that the fuel pressure regulator be disconnected from the vacuum line. It was also suggested that I shouldn't do that and so I hooked it back up again. No difference either way. The engine is running lean according to what the diagnostic machine read. Still no codes showing and the car runs basically really good inspite of the miss. I did forget to mention above the ECM and a Hypertech chip were recently replaced also. I continue to drive the car in hopes the the ECM is still in the learning stage and will correct things, so far it hasn't. Any other suggestions would be greatly appreciated. Thank you all for previous suggestions.

 

[DarkRed89Flyer]

I replaced the o2 sensor and checked the grounds recently and I still have the slight miss plus a little surge at times. I was wondering if the ESC has anything to do with it. It has never been replaced. I disconnected it while the car was running at idle and nothing happened. As it now stands the complete fuel system has been replaced from pump to injectors. The ignition has had all new plugs, wires, complete dist., and timing is set to TDC. The EGR was replaced and I checked for vacuum leaks with the propane method. It happens in both open and closed loops. The TPS seems to be operating ok and is set to specs. The IAC was cleaned along with the throttle body when the new injectors were installed. The MAF, IAC, ESC, and TPS are the orignals. Because I have the Bosch Gen III injectors it was suggested that the fuel pressure regulator be disconnected from the vacuum line. It was also suggested that I shouldn't do that and so I hooked it back up again. No difference either way. The engine is running lean according to what the diagnostic machine read. Still no codes showing and the car runs basically really good inspite of the miss. I did forget to mention above the ECM and a Hypertech chip were recently replaced also. I continue to drive the car in hopes the the ECM is still in the learning stage and will correct things, so far it hasn't. Any other suggestions would be greatly appreciated. Thank you all for previous suggestions.

FForward, I have a similar situation with my '89, except that in addition to a rough idle, the engine will stall, almost like someone is turning off a light switch. There's no warning and it's immediate. I, too, have replaced all of the ignition components, including the ESC module and entire distributor assembly, to no avail. I've checked the ground-point on the bell housing. I've also replaced the EGR Valve, valve control solenoid, and all of the associated vacuum lines. I tested the TPS for flat- or dead-spots and got consistent readings. Fuel pressure is constant at 42psi. A shop that I took it to, to replace the distributor, told me that the #6 injector wasn't firing, so I replaced that too and checked the signal with a noid light. When I bought the car a few months ago, it ran great. I've driven it to California, Las Vegas and Mexico, but since it developed this stalling issue, I haven't driven it anywhere. It hasn't been on the road since Easter Sunday, except on the back of a flatbed tow truck. Like you, I don't trust it, and until I can figure out what is causing this situation, it's staying parked in the driveway. This weekend, I plan to replace all of the gaskets associated with the air intake plenum and runners. Another mechanic I spoke to said that if there is any "extra" air getting into the intake that isn't being measured by the MAF, it could be causing the rough idle & the stalling. I'm not sure I agree, but in an attempt to rule it out, and because of the car's age, I thought this might be a cheap fix, if it works. Besides, the gaskets look like they're originals. I also have a similar thread, if you want to read any of those suggestions. It is: http://www.corvetteactioncenter.com...formance/126912-what-causing-my-89-stall.html

 

[boomdriver]

the injectors are plugged or dripping and not spraying...

the issues are in the fuel system

 

[FForward]

You said you replaced one bad injector. In order to replace one you have to pull the plennum and runners to get at the fuel rails. Wasn't new gaskets used when you did that? If the rest of the injectors were stock they are Multitechs and are junk. Was the one replaced a Multitech or another type? If it was a different type you have a miss match which would possibly cause some problems. One problem I had with my stock injectors was the car ran fine, then wouldn't restart after a few minutes. After sitting for an hour or more it restarted and seemed fine again. I checked the resistance on all of them and found some that were real low. I got a set of Bosch Gen III's from Fuel Injection Connection and installed them with all new intake gaskets. Jon at FIC told me to either get a adjustable fuel pressure regulator or pull the vacuum line off of it and plug it. The reason was the new injectors ran at higher pressure than the stock ones. The car ran amazingly better than it ever did before. I was later told that pulling the vacuum line off was a bad idea, so I reconnected it. That didn't work out so good, as I stepped on the pedal to pass, the car would fall flat and then take off. I disconnected that vacuum line and its back to running normal again. Running fuel cleaner thru the stock injectors only worsens the problem. The coils in the Multitechs are in the fuel stream and the cleaner eats away at the insulation shorting them out or reducing their resistance. Your best bet would be to replace all the injectors with the Bosch ones install all new gaskets and pull that vacuum line off the regulator and plug it. You may want to change the intake manifold gasket at that time also. Mine had small amounts of antifreeze sitting on top of it and is a common problem with leaking there. I also installed a new O2 sensor and the car seems to run better and haven't had any problems so far. I used propane to check for any vacuum leaks and found none. The only things that wern't replaced was the MAF and the ESC, everything else was, including the ECM and a new chip. The car has only a slight miss now that is hardly noticed and I think the ECM is still in the learning process and it will go away eventually. I installed a new fuel pump and screen and am running 43psi's steady to the injectors with the vacuum hose disconnected to the regulator. The Multitechs ran at lower pressures than the Bosch do. Hope this helps you as I know how it feels to drive it and wonder if you'll be getting it back home again. Good luck and let me know if this solves your problem....Bill

 

[DarkRed89Flyer]

You said you replaced one bad injector. In order to replace one you have to pull the plennum and runners to get at the fuel rails. Wasn't new gaskets used when you did that? If the rest of the injectors were stock they are Multitechs and are junk. Was the one replaced a Multitech or another type? If it was a different type you have a miss match which would possibly cause some problems. One problem I had with my stock injectors was the car ran fine, then wouldn't restart after a few minutes. After sitting for an hour or more it restarted and seemed fine again. I checked the resistance on all of them and found some that were real low. I got a set of Bosch Gen III's from Fuel Injection Connection and installed them with all new intake gaskets. Jon at FIC told me to either get a adjustable fuel pressure regulator or pull the vacuum line off of it and plug it. The reason was the new injectors ran at higher pressure than the stock ones. The car ran amazingly better than it ever did before. I was later told that pulling the vacuum line off was a bad idea, so I reconnected it. That didn't work out so good, as I stepped on the pedal to pass, the car would fall flat and then take off. I disconnected that vacuum line and its back to running normal again. Running fuel cleaner thru the stock injectors only worsens the problem. The coils in the Multitechs are in the fuel stream and the cleaner eats away at the insulation shorting them out or reducing their resistance. Your best bet would be to replace all the injectors with the Bosch ones install all new gaskets and pull that vacuum line off the regulator and plug it. You may want to change the intake manifold gasket at that time also. Mine had small amounts of antifreeze sitting on top of it and is a common problem with leaking there. I also installed a new O2 sensor and the car seems to run better and haven't had any problems so far. I used propane to check for any vacuum leaks and found none. The only things that wern't replaced was the MAF and the ESC, everything else was, including the ECM and a new chip. The car has only a slight miss now that is hardly noticed and I think the ECM is still in the learning process and it will go away eventually. I installed a new fuel pump and screen and am running 43psi's steady to the injectors with the vacuum hose disconnected to the regulator. The Multitechs ran at lower pressures than the Bosch do. Hope this helps you as I know how it feels to drive it and wonder if you'll be getting it back home again. Good luck and let me know if this solves your problem....Bill

Bill:

I did as you suggested and bought a whole new set of injectors, although I didn't get them at FIC. After spending several hundred dollars doing that, it didn't solve the issues. I still have the rough idle and a lean condition. However, I did solve the stalling problem. Come to find out, the spark plugs installed, when the first shop did the "standard fix," which really didn't fix anything, were defective, or incorrectly installed. Two of them had cracks in the ceramic insulator and were apparently grounding out. The #1 and #2 cylinders were both affected. It makes me think that the tech over-torqued them while installing them. Not for lack of trying, but I've resigned myself to just putting up with the rough idle because none of the shops I've taken it to can seem to find a reason for the rough idle. Like you, I've replaced the entire ignition system, including the coil, distributor, ignition module and ESC, the fuel filter & pump strainer, the EGR valve, the valve solenoid and all associated vacuum lines, and checked the engine grounds and TPS. The last shop I took it to (the ones who found the screwed up spark plugs) did some kind of special test to check for air leaks around the runners and plenum and couldn't find any leaks there either. The only thing I haven't changed is the MAF sensor, which the last shop supposedly cleaned while cleaning the IAC. The only other thing I haven't changed is the O2 sensor, but on a recent trip from here in Mesa to Las Vegas, I averaged 28MPG, including driving on "The Strip," which as you probably know is bumper-to-bumper traffic on the weekends, and that was with the A/C on the entire trip.

 

[John Robinson]

A couple of things you may have overlooked. The wire connectors to the MAF, TPS, IAC, and a couple of other sensors have very small wires. I have had problems with my 93 and those wires breaking with the removal of the connectors to replace the sensors. It is easy to forget the age they have on them and the fact that they can break. Somewere the grounds for them all come together in a bundle. Unwrap that bundle and separate the wires. Then trace them to there respective sensors and do a continuity check of each wire and connector. I am guessing but I think you will find a broken ground wire on the IAC or TPS.


DO NOT BACK PROBE THE ECM. THE CURRENT FROM THE METER BATTERY COULD BE FATAL TO THE ECM.