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1991 Rough Idle/Misfire

S

sollaris

Registered Member
Joined
16 September 2009
Messages
77
Location
Arlington, TX
Have a rough idle and possible misfire on my 91. She only has 54K miles and the TB,WP, Belts, and such were done last year and i have only put around 4K miles on her since then. I checked all the plugs and tested all the coil packs and everything is fine there. Did a compression test and the front bank is ~210, Rear ~185. Also did a leak down test on the rear 3 and everything was fine. This seems like its a little over the normal range. Would this cause a misfire and the rough idle i am experiencing or could they be 2 separate problems? I am assuming i should get a valve adjustment.

I have been reading around and the misfire could be a number of things that i am running through and checking beyond the coil packs and spark plugs but wanted to know if anyone else has run into a similar situation or if anyone had some ideas as to where else i should look. There are no codes on the ECU.
 
If you had an actual misfire, the ECU would probably throw a code. Rough idle could be a dirty throttle body, partially clogged injector, bad O2 sensor, etc. It would help to provide a more thorough description. Does it happen only when idling and does it go away when increasing the engines rpm's? Did any of the spark plugs electrodes look different? Do you have fresh gas? Too many variables to say really :confused:.
 
Did this problem start after the TB/WP? Looking at those compression numbers I think you may have a cam that is a tooth off on the rear bank. If it were a head gasket on the rear bank the leak down would have shown that unless it only leaks when the engine is warm. A cam that was a tooth off would cause a rough idle but then so can a dirty throttle body. A good test is to hook up a vacuum gauge up while it is running. Comparing the results to online guides or included instruction sheet should let you know whether your valve timing is off or ok.

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm
 
Last edited:
pgilliam1 said:
If you had an actual misfire, the ECU would probably throw a code. Rough idle could be a dirty throttle body, partially clogged injector, bad O2 sensor, etc. It would help to provide a more thorough description. Does it happen only when idling and does it go away when increasing the engines rpm's? Did any of the spark plugs electrodes look different? Do you have fresh gas? Too many variables to say really :confused:.
Click to expand...

Happens only when idling, it goes away as i get on the gas. I replaced the O2 sensors when i did the TB/WP service as the car did not pass inspection before that. All the the spark plugs looked the same when i pulled them out. Gas is probably a couple of weeks old, but i dont think thats it. I plan on pulling out the injectors and cleaning, we will see if that helps anything.
 
Have you checked the Idle Air Valve or cleaned the throttle body?
 
Where is the Idle Air Valve?
I am going to clean the Throttle Body, and check all the injectors tonight.

Thanks for the suggestions guys keep em coming please.
 
I have ran into this problem with my 95. If you get bad fuel, it will idle rough and misfire for that full tank. Try new gas, and clean the throttle body
 
Somehow i missed your first post Edin. I'll try the vacuum test. The TB/WP was done over a year ago, i dont think it has been doing this that long. I am trying to run through everything i can do before engaging the dealer a year later and telling them that they might have screwed up and having to deal with that mess.

I cleaned the Throttle Body and dropped some Sea Foam in the tank to clean the injectors, it made no difference. With the compression being off a little over the normal range i think my next step is the vacuum test.

Thanks.
 
I really don't like those compression numbers. I'm suspicious that the timing on one of the cams is off a tooth. Perhaps Larry B. can chime in here.

Gary
 
Well i have scheduled time to have the valves adjusted and have them look at the timing at the same time. I hope they find something...

Ill keep you posted.
 
Seems that the timing was indeed off a couple teeth. Also looks like the tensioner was not installed correctly either. Getting the car back tomorrow and will let you know if it fixes the issues i was having.

Just as a side note NEVER bring your car to Goodson Acura in DFW for service. I will be posting a lovely note in the other section about my experience with them.
 
Bring the bill to the Acura dealer and ask them to pay for the service. They obviously caused the problem (if it fixes it) by not tensioning the belt correctly. Good Luck!
 
Got the car back today. Timing issue is fixed and compression tests good all the way around. Had to replace the tensioner as it was not installed properly, and the timing belt was off a tooth on the rear cam.


Still runs a little rough at idle though... Any other ideas on that? I cleaned the Throttle Body before i took it in, so i don't think that's it.

Thanks for all the help pointing me to the timing belt.
 
pgilliam1 said:
If you had an actual misfire, the ECU would probably throw a code. Rough idle could be a dirty throttle body, partially clogged injector, bad O2 sensor, etc. It would help to provide a more thorough description. Does it happen only when idling and does it go away when increasing the engines rpm's? Did any of the spark plugs electrodes look different? Do you have fresh gas? Too many variables to say really :confused:.
Click to expand...

FYI: No misfire detection on a 1991, only 1995+ OBDII;)
 
Last edited:
sollaris said:
Got the car back today. Timing issue is fixed and compression tests good all the way around. Had to replace the tensioner as it was not installed properly, and the timing belt was off a tooth on the rear cam.


Still runs a little rough at idle though... Any other ideas on that? I cleaned the Throttle Body before i took it in, so i don't think that's it.

Thanks for all the help pointing me to the timing belt.
Click to expand...

All NSX's are a litle rough at idle. 1300RPM is about the max roughness.

Regards,
LarryB
 
sollaris said:
That's probably it then. It idles anywhere between 1300-800.
Click to expand...

Is it fluctuating between those RPM's? or is it steady but between those values? If it is fluctuating, you most likely have a vacuum leak somewhere.
 

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