Rb26dett High Idle And Miss Firing

[gucio]

Hi All

This abit of a long story, sorry.

Ok this is the history behind the problem. I decided that it would be a good idea to pull out the engine so I can replace the clutch and in the mean time I replaced the oil pump (N1 item), water pump (standard) and timing belt (standard). I also replaced all the seals on the intake and exhaust side of the engine. Injectors where ultrasonically cleaned. I have put on aftermarket dumps and front pipe. I also cleaned out the idle control unit (pulled it apart and cleaned), throttle bodies (I pulled out the butterflies to clean them), intercooler and piping including bypass valves, painted and cleaned the intake plenum. I have not touched the computer or the tuning.

So when I put the engine back in the car started to idle high (around 1200) and rough (sounds like it is back firing). So I searched thought the forum and searched everything from rough idle to how to adjust idle, I have tired the following to no avail:

- Cleaning AFM’s

- Replaced spark plugs (to iridium tip NGK ones)

- Checked timing belt marking so they match up twice

- Did a computer diagnosis check which came up with a faulty TPS.

- Have done idle adjust procedure according to manual and FAQ guide

- Screwed the idle screw in completely.

- Checked vacuum lines (but I don’t have proper vacuum line diagram so I don’t know if they are connected in the right way)

- Pulled apart TPS and checked it too but it seemed fine.

I think that’s it.

I am trying to avoid pulling off the plenum.

So if anyone has any ideas, I am all ears. I am getting sick of the car not running.

I may have missed some details so I wrote this at work and I keep getting interrupted.

[GTR32GUS]

If the diagnosis told u the TPS is farked then replace it

[gucio]

I understand that i should replace it, but would it cause the above problems?

[GTR32GUS]

i had problems with a high idle a while ago the hose which comes off the intake manifold had a crack in it , this made my car run rough as well so i would be double check all the air hoses , im not sure what a broken TPS causes

[gucio]

Does any one have a picture or a diagram of the vacuum lines casue I am not sure if what I have done is correct. I do have one from the manual but that isnt comprehension enough.

Crack, how did you find that?

[SLIPPERY]

spray some water or wd-40 around the place such as hoses and seals.

If you hear the idle decrease for a bit then youve found a vacuum leak.

Thats a good way to find a leaky/cracked hose

[SLIPPERY]

my bad idle is due to the stepper motor being shagged

thats another alternative solution to your idle problems perhaps

[johnnyt]

when you cleaned the throttle butterflys did you make sure you could not see any light through them when you put them back in?

had that problem with mine after i cleaned them i had to take the plenum off to re adjust the throttles.

johnny

[blind_elk]

You shouldn't clean the throttle bodies. They rely on the buildup of crap to help seal the butterflies at idle.

[gucio]

Ok update, I brought a new TPS and installed it, the car idles abit better but still high and rough. Checked the computer and now says TPS and knock sensor error.

Whats a stepper motor? is that the distributor?

When i put the butterflies back in they didnt seems to sit properly. and yeah there was light coming through.

Are you serious about not cleaning the butterflies?

[SLIPPERY]

the tuner referred to it as the stepper but he means the IAC valve

If you can see light then gas will get sucked through there

i think youve answered your own topic

[gucio]

I understand that the butterflies would cause higher then normal idle, but what would cause rough/miss firing sorta idle?

[SLIPPERY]

a lean mixture from sucking in too much air

[Zerrun]

I had a slight missfire was due to the seals between the turbo intake manifold @ the plenum, also the ones between plenum and motor being buggered, new seals stopped the misfire might pay to check yours

[gucio]

ok will try the wd-40 idea tonight and see what happens

I have new seals on both the intake and exhaust side, can i use the above method to check for leaks?

[SLIPPERY]

id try water in something you could get a decent amount of fluid onto the hoses with

wd-40 sprays out at a pretty pissy rate

[gucio]

Another update, I took off the intake plenum and the butterflies have a very slight gap on the top and bottom, does anyone know how to get the butterflies to close properly? do i just pull them out and try to find the throttle body that they fit into correctly?

[89_SIL]

Ok update, I brought a new TPS and installed it, the car idles abit better but still high and rough. Checked the computer and now says TPS and knock sensor error.

Whats a stepper motor? is that the distributor?

When i put the butterflies back in they didnt seems to sit properly. and yeah there was light coming through.

Are you serious about not cleaning the butterflies?

I need a new TPS for my RB20. Mine idles really high aswell, but not rough. Where did you get ur TPS and where can I get one for an RB20?

[gucio]

I brought my TPS from Nissan ($130), but I know you can also get one from Coventries.

I am from Perth by the way.

[blind_elk]

I need a new TPS for my RB20. Mine idles really high aswell, but not rough. Where did you get ur TPS and where can I get one for an RB20?

Morgan, your problem is possibly an out-of-alignment TPS not sending a "throttle closed" signal to the ECU. Does the engine tend to maintain revs on gear changes?

The fix has been covered - search.