Car staying at Idle Does not accelerate

[NSX~PERT]

I went to get into my 91 today and the car started right up but when I went to accelerate it nothing happened. It remained at idle. I checked the obvious throttle cable is intact and is working and the throttle body is moving back and forth but no acceleration at all. Can the TPS or actuator be bad? Any suggestions

 

[Old Guy]

All of the following comments were predicated on a stock engine running a stock ECU. After writing them I re read your post and noticed in your signature that you have a singe turbo. That is a big red flag that potentially changes everything. Are you running a stock throttle body and manifold with MAP based fuel control? I am guessing that you are no longer running a stock ECU with diagnostics?

The engine will normally function OK with the throttle position sensor disconnected. Its primarily there for acceleration enrichment, wide open throttle indication, flood clear and fuel cut functions.

Not sure what "throttle body is moving back and forth" means because the throttle body can't move. Pull the bellows off and check the operation of the throttle plate / blade to confirm that it is opening and closing. If the throttle plate is opening and closing then I vote for a problem with the MAP sensor. However, a failed MAP sensor would make the engine hard to start unless it is quite warm. I expect that a MAP sensor failure will put the ECU into limp mode. Normally, if the MAP sensor fails the ECU would generate an error code and you would illuminate the MIL. Use the service check connector to check for stored codes. It is also possible that the vacuum line connecting the MAP sensor to the intake manifold has split or has come loose.

 

[Spoolinfool]

Do as Old Guy says list all the modifications and anything you have last done when you touched it. Also how long it has been since it has last been driven/ in storage. These car are rock solid and most of the issues come from our modifications unfortunately.

 

[NSX~PERT]

All of the following comments were predicated on a stock engine running a stock ECU. After writing them I re read your post and noticed in your signature that you have a singe turbo. That is a big red flag that potentially changes everything. Are you running a stock throttle body and manifold with MAP based fuel control? I am guessing that you are no longer running a stock ECU with diagnostics?

The engine will normally function OK with the throttle position sensor disconnected. Its primarily there for acceleration enrichment, wide open throttle indication, flood clear and fuel cut functions.

Not sure what "throttle body is moving back and forth" means because the throttle body can't move. Pull the bellows off and check the operation of the throttle plate / blade to confirm that it is opening and closing. If the throttle plate is opening and closing then I vote for a problem with the MAP sensor. However, a failed MAP sensor would make the engine hard to start unless it is quite warm. I expect that a MAP sensor failure will put the ECU into limp mode. Normally, if the MAP sensor fails the ECU would generate an error code and you would illuminate the MIL. Use the service check connector to check for stored codes. It is also possible that the vacuum line connecting the MAP sensor to the intake manifold has split or has come loose.

Sorry should of added that. It has a single turbo running a AEM ECu no longer a OEM. Car had been sitting for about a month since I last drove it fine. I went to go move it in my shop and it started right up but no acceleration. I meant by the throttle moving back and fourth the throttle blade. I was going to take off my intercooler to investigate that next bit wanted to get on here to see if anyone has had a similar issue. Im attaching a video of when it started right up and nothing changes when I accelerate it. How can I test the MAP sensor to see if this is the culprit?

 

[Old Guy]

If you are running AEM I would assume that you have the AEM interface software? This should allow you to see what the MAP sensor is reporting in terms of manifold pressure while the engine is running. Opening the throttle should cause the manifold pressure to change which should show up on the interface if the MAP sensor is working. If the manifold pressures look correct then the problem is probably someplace else.

If you are still running the original MAP sensor you could do the basic tests described on page 11-44 of the 1991 service manual. However, that test is for a MAP sensor that does not run above 100 kPa. I expect you have a sensor designed for > 100 kPa so you would need to know what the voltage slope characteristics are for your sensor. With the voltage slope for your sensor, a voltmeter and one of those little hand held vacuum pumps you can test your sensor to find out whether it is working. If you don't have the voltage slope characteristic for the sensor you are kind of screwed. You can use the vacuum pump to find out whether the sensor is leaking which is a mechanical failure as opposed to the sensor element going out of calibration.

 

[Spoolinfool]

I'd pull the intercooler and check for restrictions before the throttlebody and check for throttlebody operation.Probably not a bad idea to go in there with a scope and check your intake bypass butterfly screws. If all checks out I'd reload the map again on the aem and try again. These aftermarket computers the files can become corrupt and give off weird issues and reloading the maps fixes them.Other than that Id check for rodents making nest both on the turbo inlet side and the exhaust side.

 

[Old Guy]

With respect to the MAP sensor, in addition to checking the actual sensor and the vacuum line I suggest you check the continuity of the wiring between the sensor and the ECU. If you have the AEM interface software that would also normally allow you to observe the throttle position which could be an indicator of problems with the throttle plate.