HELP rough idle 89 Corvette
#1
HELP rough idle 89 Corvette
I have a 89 Corvette that has developed a rough idle once the engine warms up. Vehicle has 43000 miles. I have replaced fuel pump, fuel filter, plugs , wires, pick up coil, cap, rotor , TPS , IAC , O2 sensor, ESC module and ECM. Problem remains the same. Took it to the dealership and they had their "best guy" spend hours trying to find the problem. They could find nothing. Ruled out injectors , vacuum leaks and all the easy stuff. When you unplug the Set timing connector the miss goes away and the vehicle idles fine. No codes .
Only thing I know left to replace is the PROM and the MAF sensor.
Anyone had similar problems or any ideas.
Any help would be greatly appreciated.
Only thing I know left to replace is the PROM and the MAF sensor.
Anyone had similar problems or any ideas.
Any help would be greatly appreciated.
#3
Team Owner
What did they do to rule out the injectors? Sounds like you replaced everything else but the MAF and EPROM. Have you scanned it for what the IAC counts are like on a warm idle? I'd let you use my ECM but it wouldn't work and neither will the EPROM but someone should have those and a known good MAF to test.
Before I throw those things you did at it, I'd dump the injectors and get rebuilt ones that are cleaned and tested. You never know if the pintles are dirty unless you bench test them
Before I throw those things you did at it, I'd dump the injectors and get rebuilt ones that are cleaned and tested. You never know if the pintles are dirty unless you bench test them
#4
Le Mans Master
..... Keep throwing new parts at it , you will eventually stumble on the problem and maybe fix it .....
..... FYI ... There is a diagnostic flow chart in the Factory Service Manual that might prove to be quite helpful ... I'll bet a 12 pack of your favorite brew that the dealer's "best guy" did not have access to the correct FSM .....
..... FYI ... There is a diagnostic flow chart in the Factory Service Manual that might prove to be quite helpful ... I'll bet a 12 pack of your favorite brew that the dealer's "best guy" did not have access to the correct FSM .....
Last edited by C409; 07-23-2016 at 09:23 PM.
#5
Drifting
I have a 89 Corvette that has developed a rough idle once the engine warms up. Vehicle has 43000 miles. I have replaced fuel pump, fuel filter, plugs , wires, pick up coil, cap, rotor , TPS , IAC , O2 sensor, ESC module and ECM. Problem remains the same. Took it to the dealership and they had their "best guy" spend hours trying to find the problem. They could find nothing. Ruled out injectors , vacuum leaks and all the easy stuff. When you unplug the Set timing connector the miss goes away and the vehicle idles fine. No codes .
Only thing I know left to replace is the PROM and the MAF sensor.
Anyone had similar problems or any ideas.
Any help would be greatly appreciated.
Only thing I know left to replace is the PROM and the MAF sensor.
Anyone had similar problems or any ideas.
Any help would be greatly appreciated.
#6
Thanks everyone for the posts !
The GM dealer assured me it was not the injectors and that the IAC was doing what it should. I don't think that they had the exact diagnostic scanner needed due to the age of the car. I think the car is older than the guy who worked on it ! But I told them that I had checked the Ohms(hot and cold) on the injectors and they were within specs. They said they had done some other kind of test on them and they were fine. They are not the original injectors.
Again the car runs fine other than the rough idle and that goes away when you disconnect the Set timing connector. Would a bad MAF sensor cause this ?
I am new to this forum and any and all posts are appreciated.
The GM dealer assured me it was not the injectors and that the IAC was doing what it should. I don't think that they had the exact diagnostic scanner needed due to the age of the car. I think the car is older than the guy who worked on it ! But I told them that I had checked the Ohms(hot and cold) on the injectors and they were within specs. They said they had done some other kind of test on them and they were fine. They are not the original injectors.
Again the car runs fine other than the rough idle and that goes away when you disconnect the Set timing connector. Would a bad MAF sensor cause this ?
I am new to this forum and any and all posts are appreciated.
#7
Team Owner
The GM dealer assured me it was not the injectors and that the IAC was doing what it should. I don't think that they had the exact diagnostic scanner needed due to the age of the car. I think the car is older than the guy who worked on it ! But I told them that I had checked the Ohms(hot and cold) on the injectors and they were within specs. They said they had done some other kind of test on them and they were fine. They are not the original injectors.
Again the car runs fine other than the rough idle and that goes away when you disconnect the Set timing connector. Would a bad MAF sensor cause this ?
I am new to this forum and any and all posts are appreciated.
Again the car runs fine other than the rough idle and that goes away when you disconnect the Set timing connector. Would a bad MAF sensor cause this ?
I am new to this forum and any and all posts are appreciated.
It could be the MAF is bad however, before I go that route, I would try borrow one from someone in your area to test. Swap them and run them both. If the problem goes to his car, there is your answer.
If you send them to FIC and they say they are Multec, they can be rehabbed but I'd toss them. Ethanol eats away at the coils so dump them for the Bosch injectors. Get a reman set. My testing shows they get dirty within 3 years of use so that is about how long before I send them in for cleaning and testing.
Get yourself a Factory Shop Manual and a scanner. FSM can be had on ebay for your year. Get a scanner and NOT a code reader. You want to be able to see the data your ECM sees. With a scanner we can guide you through the testing. Without, we can guess.
Last edited by aklim; 07-24-2016 at 12:23 PM.
#8
Le Mans Master
You like many keep your location secret. Look for help from local corvette, f body, or impala ss, fleetwood club for help finding someone who knows what there doing. Without a scanner, FSM, and most likely a few more things, your unlikely to DIY. it sounds like all the easy fixes other a MAF have been taken. Disconnecting set timing connector fixes timing, ecm can raise idle to set value. Were any repairs done or did happen prior to rough idle?