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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.

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https://www.sau.com.au/forums/topic/183491-rb26dett-high-idle-and-miss-firing/
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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

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 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

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?

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?

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.

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