High Idle, 1500Rpm Very Confused

[central coast person]

Hey guys, i have a problem with my car idling at 1500rpm. I got the problem a year ago at a set of lights, my idle was hunting but only on occasion and has gotten worse ever since. Now it happens 99% of the time sometime while driving, brings up the 4WD light on my dash and its constantly at 1500rpm at idle. Obviously the ECU knows there is something wrong so its logging the fault code 75 in the ECU in the boot which is a TPS error, i always thought it was the TPS as well so i ordered a BRAND NEW one and installed it tonight and still have this problem......

Car is fairly stock and i work for nissan parts so everything i fit is brand new, its got a Apexi pod filter, i have rebuilt it changing it from 2.5L to 2.7L, full gasket kit, Air flow meter, IACV (2nd air regulator), TPS, 90% of the engine internals .......... loads more bits and pieces and that's just on the engine! Basically the car doesn't even have 1 broken clip in it. The only thing i have not changed is the alternator , coolant temp sensors, Crank angle sensor , injectors, coilpacks.....(all tested and are spot on what the need to be) i haven't changed the AAC valve as i cant figure out the specs for testing it.

My new and old TPS's are both 0.4V when tested with a multimeter and when fully open are 5.0V so both are what the manual says. I can make it idle as if TPS has not problem at all, i twist the TPS almost all the way to the right and from 1500RPM its just plunges back to the stock 650RPM. In doing so i check the consult to see the voltage its been changed to when adjusting and its 0.22V not the stock 0.4V,anything over 0.22V and it jumps to 1500RPM. So i cant understand why i have to adjust the TPS to a lower voltage to make the car idle like there's no problem at all ..... maybe related to car almost stalling when i stop at the lights, i cleaned the AAC 3 times to try fix this but it only improved the car slightly so all i can guess is the AAC valve is finished.

any input would be good, cheers.

Edited June 16, 2011 by central coast person

[DVS JEZ]

What ecu

[central coast person]

Its just a stock one, never been touched, never pulled the plug out on it either. The rear ATTESSA ecu logged the fault but as the TPS is part of the circuit in the ATTESSA system.

[blind_elk]

The TPS has 2 parts - a SENSOR, which tells the ECU how much throttle is being applied, and a SWITCH, which tells the ECU that the throttle is closed.

Your description

i twist the TPS almost all the way to the right and from 1500RPM its just plunges back to the stock 650RPM

suggests that the SWITCH component isn't set correctly. I think it is pins 1 & 2 - ohms should be 0 when throttle closed, and not 0 when you crack the throttle open.

[central coast person]

Yeah i can see that in the manual how its a switch and sensor in one and 2 different tests. Its 0 ohms when fully closed and changes when you apply throttle, i cant see why i have to set the TPS to a very low voltage (0.22V) to get a good idle when the factory says 0.4V at idle, either way adjusting the TPS has no change in ohms only voltage, it only changes ohms when i give it throttle and it twists the mechanism on the back of the TPS.

[DVS JEZ]

2.7l with a stock ecu. . Better be carefull with the stock tune

[Muff]

agreed, cant expect the car to run properly if you stroke it to a 2.7 with a stock ecu....

[mad082]

+1 for running a stock ecu on a 2.7L engine not helping the situation.

[karma_syke]

leaky throttle body?

[blind_elk]

... i cant see why i have to set the TPS to a very low voltage (0.22V) to get a good idle when the factory says 0.4V at idle...

Maybe there's some wear in the sensor contact that causes a lower than factory voltage reading.

Did you measure ohms on the other pair of pins - one way or the other, there will be 0 ohms @ throttle closed.

At the end of the day, if 0.22V causes the idle rpm to be at a reasonable level, then who gives a rats about what the manual says?

[central coast person]

It would'nt be the ECU for a 2.7 non turbo, it was fine for the first 6 months after the rebuild with not 1 problem and felt stock. Checked for leaks but i have all new gaskets and pipes on the car, the throttle body is not leaking either, tried setting idle again and it just went up to 1500rpm. i spun the throttle position sensor all the way around to make an error so the car would idle at the 750 mark, definatly has to be the AAC-IACV valve because it seems like the motor is stepping up the idle because it thinks the TPS is faulty, so i have ordered one to see if i can fix it. Will post back if it fixed it.

[sneezy]

I have 32gtst with the same problems. I tried adjust my TPS and it seemed to do was make the idle climb to 2000rpm. I also disconnected the IACV to see if it was causing the high idle but appeared to do nothing, it still idled at 1100rpm. I was thinking it may be an AFM problem? It has me stumped & I'm asking around so I will post any suggestions I hear of.

[central coast person]

cheers man, Yours is only idling to 1100rpm so its sounds more like a vaccume leak more than anything, AFM cause a low lumpy idle not a high idle. Also a stuck open cold start regulator is just as plausable as a vac leak. My cars cold start was faulty and it idled around 1100rpm and when i changed it it only idled that high at cold start and came down to 700 once warm so check those two things first.

i just changed the AAC-IACV valve and it didnt fix the problem but its changed the problem for me, my car only does this now when i have an electrical load on the engine!!!!!!

I turn my headlights on and it goes to 1500rpm and i turn then off and it drops back to 700.........then if i use something else electrical like putting my rear demister on and maybe my indicator or use my brake or even the interrior lights it will also make the idle rise once i hit a certain electrical load on the engine. Once i turn something off it lowers the electrical load and my idle just drops straight back to 700rpm where it always has been and i want it.

P.S. the tps is now adjusted to 0.4V at idle with the new AAC-IACV and it is not causing the idle issue or bring up a fault anymore. But i want to fix this because i cant really drive at night because my car idles so high and bucks and runs rough when there is an electrical load

[iruvyouskyrine]

I have 32gtst with the same problems. I tried adjust my TPS and it seemed to do was make the idle climb to 2000rpm. I also disconnected the IACV to see if it was causing the high idle but appeared to do nothing, it still idled at 1100rpm. I was thinking it may be an AFM problem? It has me stumped & I'm asking around so I will post any suggestions I hear of.

Yep, 32 gts-t here and same problems. Will be cleaning my AAC valve and seeing if that makes a difference.

[central coast person]

Yep, 32 gts-t here and same problems. Will be cleaning my AAC valve and seeing if that makes a difference.

change your cold start regulator, it will fix it. i work for nissan and can order one for you if you want

[central coast person]

I have 32gtst with the same problems. I tried adjust my TPS and it seemed to do was make the idle climb to 2000rpm. I also disconnected the IACV to see if it was causing the high idle but appeared to do nothing, it still idled at 1100rpm. I was thinking it may be an AFM problem? It has me stumped & I'm asking around so I will post any suggestions I hear of.

Yeah, i have not changed my CAS or AFM, i really have changed like everything else to brand new in my car, no tech at work knows what it is and wont fault ........ I guess it could be the soldering for the hot wire in the AFM as my car has a lumpy start in the morning like my AFM is un pluged.

[central coast person]

Set my TPS at 0.40V for a few weeks now and problem is not as bad but its will still happen if i use my headlights and degmister and rear brake lights all at once. Its an electrical load thing. It wont happen when i pull a sensor out and fault the car until i turn it off and turn it back on. Also when all out and got a new AFM............all i have now is CAS and Coils............ so pissed off with this problem as driving in the rain i have to choose to not have one of these on and if i do my car is so hairy to drive around corners slowly as is wants to buck and kick.

[blind_elk]

If it happens when you load the electrics, then that suggests a problem with the alternator. Or possibly a bad earth.

[central coast person]

Blind_elk after 2 years i found it last night. Its was the earth to the starter motor, it had been painted when at the panel beaters i guess and stuck back ontop of the paint so im pretty frigen happy after changing all the sensors in the car. Cant believe how often people stuff up with skylines when you dont work on it yourself.

Cheers everyone for the input.

[simpletool]

No that's just people stuffing up with cars in general. Unfortunately most people only have a narrow training focus and have no care in the world about topic that do not relate precisely to them. This is especially prevalent in Australia where specific knowledge is high but general intelligence is lacking.

Glad you found the fix. However I see the factory service mentality of just replacing every part possible has bitten you on the arse. Sorry to hear.