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91 nsx have rough idle
- Thread starter Almejohn
- Start date
Is this a cold start, a hot start problem or does it occur all the time?
If you press down on the throttle slightly can you get the engine to hold its RPM around 800 - 900 RPM with steady operation? If so and since your car is a 1991, my knee jerk reaction is that you may have a problem with the electronic Idle air control valve (EACV) . The problem could be a failed valve which should set a diagnostic trouble code (use the service check connector to check for codes); but, is more likely to be a sticking valve which can be remedied by cleaning. It could also be:
- crud in the air passages in the throttle body that lead to the EACV
- crud in the air passages that lead to the warm up valve and the idle speed set screw
- a problem with the warm up valve if this is just a cold start problem
If you search you can find threads on Prime discussing cleaning of the EACV and cleaning of the throttle body. Note that just spraying TB cleaner into the throttle body will not get the idle air passages clean. Go to the NSX Prime Library (red banner at top of page) and you will find links to the 1991 factory service manual. Down load the manual and in section 11 (Fuel System) there is a whole sub section covering the idle control system. Familiarize yourself with the system including the trouble shotting / diagnosis page.
As a Moderator I am going to move this to the Do it Yourself Forum which is probably more appropriate.
If you press down on the throttle slightly can you get the engine to hold its RPM around 800 - 900 RPM with steady operation? If so and since your car is a 1991, my knee jerk reaction is that you may have a problem with the electronic Idle air control valve (EACV) . The problem could be a failed valve which should set a diagnostic trouble code (use the service check connector to check for codes); but, is more likely to be a sticking valve which can be remedied by cleaning. It could also be:
- crud in the air passages in the throttle body that lead to the EACV
- crud in the air passages that lead to the warm up valve and the idle speed set screw
- a problem with the warm up valve if this is just a cold start problem
If you search you can find threads on Prime discussing cleaning of the EACV and cleaning of the throttle body. Note that just spraying TB cleaner into the throttle body will not get the idle air passages clean. Go to the NSX Prime Library (red banner at top of page) and you will find links to the 1991 factory service manual. Down load the manual and in section 11 (Fuel System) there is a whole sub section covering the idle control system. Familiarize yourself with the system including the trouble shotting / diagnosis page.
As a Moderator I am going to move this to the Do it Yourself Forum which is probably more appropriate.
Ok thanks for the help! Update I changed the idle air control valve and also the eacv and cleaned out the throttle body and idle screw passage. It doesn’t surge on idle anymore as much but when I put it on gear the rpm drops really low. It’s automatic transmission and it only does it on drive and reverse not on neutral or park
Go to the link in the NSX Prime Library (red banner along top of web page) that takes you to the 1991 service manual and down load a copy. In section 11 there is a sub section that deals with the idle control system. Read it. As a starting point I suggest that you confirm that the transmission neutral / park signal to the ECU is working (page11-76) and then go through the procedure for setting the base idle speed (page 11-84).
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