1991 Engine rough Idle
Thread Starter
Instructor
Joined: Feb 2009
Posts: 220
Likes: 0
From: Cape Coral FL
1991 Engine rough Idle
I am the new owner of a 91 convertible with 54k miles. It was running rough and stalling. Check engine light always on. The Mech I took it to replaced the ECM. I still am dealing with an irregular idle when it warms up. It is also making a rattling/banging (for lack of a better explanation). It only happens when its warmed up for about 10-12 miles. I can also smell fuel very strong. It seems like it is loading up and not burning off the excess.
I am looking for ideas where to start and narrow this down. The mechanic is about useless, and his diagnosis is not bringing up any new codes at all. I think I may actually know a bit more than the shop at this point. Im thinking;;;; catalytic converter, fuel injectors, maybe installed a faulty ecm. just looking for ways to troubleshoot this on my own without wishing I had a good reliable mini van. When the car is just started, its hitting on all 8 runs smooth and idles perfect.
Thanks in advance for any tips.
BG
I am looking for ideas where to start and narrow this down. The mechanic is about useless, and his diagnosis is not bringing up any new codes at all. I think I may actually know a bit more than the shop at this point. Im thinking;;;; catalytic converter, fuel injectors, maybe installed a faulty ecm. just looking for ways to troubleshoot this on my own without wishing I had a good reliable mini van. When the car is just started, its hitting on all 8 runs smooth and idles perfect.
Thanks in advance for any tips.
BG
Advanced
Joined: Feb 2009
Posts: 74
Likes: 0
From: Acworth Georgia
You should take a few minutes and read the post I put up a few days ago. It's listed under "89 intermittent rough start and stalling".
I think the 91 has same set-up as my 89. Take throttle body apart and clean it. Especially the IAC area. Be careful with the pintle. Ohm the injectors and adjust the IAC and TPS. Also, go ahead and change fuel filter. If you can, check fuel pressure at the rail. You can do all this for less than 50 bucks.
Clear codes and then unplug MAF sensor. Start it up and see if it trips code 33. It did on mine. This indicates replacing MAF sensor.
I will also be replacing the injectors as soon as they get here. After almost twenty years, they are probably not working perfectly anyway. You may need to replace yours too. Call Jon at FIC. Fuelinjectorconnection.com. For 200 bucks he will send you a flow matched set of Bosch III injectors along with the gaskets to put everything back together.
Check out the videos that are posted at the top of the page regarding the injectors. I found them to be really interesting.
Hope this helps. Good luck.
I think the 91 has same set-up as my 89. Take throttle body apart and clean it. Especially the IAC area. Be careful with the pintle. Ohm the injectors and adjust the IAC and TPS. Also, go ahead and change fuel filter. If you can, check fuel pressure at the rail. You can do all this for less than 50 bucks.
Clear codes and then unplug MAF sensor. Start it up and see if it trips code 33. It did on mine. This indicates replacing MAF sensor.
I will also be replacing the injectors as soon as they get here. After almost twenty years, they are probably not working perfectly anyway. You may need to replace yours too. Call Jon at FIC. Fuelinjectorconnection.com. For 200 bucks he will send you a flow matched set of Bosch III injectors along with the gaskets to put everything back together.
Check out the videos that are posted at the top of the page regarding the injectors. I found them to be really interesting.
Hope this helps. Good luck.
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Joined: Feb 2009
Posts: 74
Likes: 0
From: Acworth Georgia
Just re-read your post. From what I've read and heard, the injectors tend to fail as they get hot. I would still do the "cheap stuff" first to see if it fixes the problem. But it sounds like you may have some injectors that are starting to fail when they get hot.
Ohm the injectors cold and then again when they are hot and see if you get really different readings. If you do, then I would bet the injectors need replacing. You'll need a digital ohm meter capable of reading on a 200 ohm scale. You'll be looking for readings around 16.
Ohm the injectors cold and then again when they are hot and see if you get really different readings. If you do, then I would bet the injectors need replacing. You'll need a digital ohm meter capable of reading on a 200 ohm scale. You'll be looking for readings around 16.
Thread Starter
Instructor
Joined: Feb 2009
Posts: 220
Likes: 0
From: Cape Coral FL
Injector test
Just Ohm tested the old injectors. (thanks for the video Jon)
6 tested at .18 and 2 tested at .007/.009.. If thats not my problem with Idling, Im sure its contributing to it.
BG
6 tested at .18 and 2 tested at .007/.009.. If thats not my problem with Idling, Im sure its contributing to it.
BG
Racer
Joined: Oct 2001
Posts: 311
Likes: 2
From: Roseburg OR
When I first got my 90 it needed a few items;
Engine would idle and run OK, but when you got on it it started to miss, a tune up fixed that, plugs, wires, cap, rotor, also replaced the coil as they do wear out.
EGR valve, had an idle problem I traced to valve not closing.
Then the injectors needed to be replaced, engine lost power, smelled rich.
The front catalytic converters were breaking apart and chunks were rattling around in front of the main cat, replaced with headers and Fowmaster force 2 for LT1
Those have been the main problems with my Toy.
Also from reading your description, the o2 sensor in the exhaust or the wire connecting it might be bad, it should also be considered a maintenance item.
Do a search for 'closed loop' to look for answers if it runs OK cold but runs rough when warm.
Engine would idle and run OK, but when you got on it it started to miss, a tune up fixed that, plugs, wires, cap, rotor, also replaced the coil as they do wear out.
EGR valve, had an idle problem I traced to valve not closing.
Then the injectors needed to be replaced, engine lost power, smelled rich.
The front catalytic converters were breaking apart and chunks were rattling around in front of the main cat, replaced with headers and Fowmaster force 2 for LT1
Those have been the main problems with my Toy.
Also from reading your description, the o2 sensor in the exhaust or the wire connecting it might be bad, it should also be considered a maintenance item.
Do a search for 'closed loop' to look for answers if it runs OK cold but runs rough when warm.
Last edited by carson; Feb 25, 2009 at 10:23 PM.
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