Hanging RPM

[Glliw]

Make sure throttle return spring is still attached. Just throwing things out there.

Yep, both the torsion spring and the linear spring are in place. I installed a secondary linear return spring to see if it was a worn spring issue but did not see to help.

[Glliw]

Here's an engine bay shot.

[Kurbycar32]

I think you should run a resistance test on your TPS sensor. A throttle position sensor is an electronic device called a potentiometer, its function is to increase in resistance as its dial is turned. Run a resistance test and when turning the dial slowly by hand watch for any erratic behavior as it indicates a bad spot in your pot

[er34gtt2000jp]

I know this sounds simple but have you checked to see if the throttle is actually retuning to closed when you let off the gas?

[Glliw]

I know this sounds simple but have you checked to see if the throttle is actually retuning to closed when you let off the gas?

Yep, it is. I pulled the AFM boot off and watched it return. Comes to a shut nicely. When the engine is not fully warmed up, say, around 1/3 temp gauge and below, a throttle blip will result in a quick rev and return to idle. The problem is greatly pronounced once at operating temperature.

[Glliw]

I think you should run a resistance test on your TPS sensor. A throttle position sensor is an electronic device called a potentiometer, its function is to increase in resistance as its dial is turned. Run a resistance test and when turning the dial slowly by hand watch for any erratic behavior as it indicates a bad spot in your pot

Between left and center pin, resistance is infinite at closed throttle and goes to zero throughout the whole range.

Between the center and right pins resistance Is zero at closed throttle and goes to infinite slightly off of closed and stays that way throughout the full range.

Between left and right pins there is infinite resistance throughout the range except for a small window of approximately 5 degrees off of closed.

[siteunseen]

Has it ever run right since you've deleted half of the the emissions and cold start systems? I've never seen anything like what you have there.

[Glliw]

Has it ever run right since you've deleted half of the the emissions and cold start systems? I've never seen anything like what you have there.

It did this before the deleting began.the deletes were part of troubleshooting.

[rcb280z]

Does happen cold and hot?

Have you checked to make sure the AFM flap is closing?

Ok I see now, open happens when warm. Seems like a BCDD issue but you said you eliminated that as a problem.

How long have you had the car? Did it do it when you bought it? etc.

Edited April 19, 2014 by rcb280z

[Zed Head]

Throttle blade hanging due to PCV gunk was an issue documented by Nissan. Addressed with a factory published remedy in a Nissan Technical Bulletin.

Just to more clearly restate what I posted before. Easy to test. Stick toe under throttle pedal and pull up when RPM are hanging high. Takes a little finesse but you can actually get skilled at it while diagnosing. If RPM drop the problem is between your toe and the throttle blade/throttle bore interface.

[Glliw]

Does happen cold and hot?

Have you checked to make sure the AFM flap is closing?

Ok I see now, open happens when warm. Seems like a BCDD issue but you said you eliminated that as a problem.

How long have you had the car? Did it do it when you bought it? etc.

Seems to happen only when warm. I have not checked the AFM.

Yes it has been an issue since Ive owned the car. I'm complaining now as I only drove it from purchase origin then to body shopwhere it sat all winter.

Throttle blade hanging due to PCV gunk was an issue documented by Nissan. Addressed with a factory published remedy in a Nissan Technical Bulletin.

Just to more clearly restate what I posted before. Easy to test. Stick toe under throttle pedal and pull up when RPM are hanging high. Takes a little finesse but you can actually get skilled at it while diagnosing. If RPM drop the problem is between your toe and the throttle blade/throttle bore interface.

That used to help. I cleaned up the space around the throttle plate and added the helper spring which helps it come down quicker initially but still slow at2.5k downward.

[Mark Maras]

I know little of the complexties of FI, being an SU guy, but there are basic similarities. I doubt the problem is fuel ratio related. The only way any engine will run at higher RPMs is increased air supply. More fuel is needed to sustain the higher revs but it starts with the air supply. Something is controlling the butterfly and preventing it from closing. Most carbs have a dashpot,(vac. diaph.) that allows the revs to fall normally, until just above idle. Think of it as a rev cushion. Whatever is causing this problem is attached to the throttle shaft or linkage and is temp. related too. Just out of curiousity how do your plugs look? It is possible running a very lean A/F ratio that an increse in fuel will raise the revs.

Edited April 19, 2014 by Mark Maras