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Running rich plus bad idle when warmed up

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Been an issue on my car for a while now and I still haven’t gotten to the bottom of it. When the engine is cold it runs fine (albeit sometimes an idle slightly higher than I think it should be), but once it’s up to temperature it really starts to stink and run rich. Quite often if I dip the clutch if I’m coasting to a stop at some traffic lights or something similar the revs will drop to around 100-200rpm then bounce back up to ~800rpm then drop down again and so on and so forth a few more times until it finally stables itself out. When it does idle at the right level it idles a little rough too.

I’ve cleaned the IACV, changed the spark plugs, had a look at the MAF but to no avail. I’m wondering, since 99% of the problem is when the car is at proper operating temperature, that it could be the coolant temperature sensor? Any easy way to test this aside from unplugging it?

Any help appreciated, cheers.
 
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An aftermarket gauge would give you an actual figure to work from. Does your car have any mods as it could need the map sorting also?
 
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Yeah an AFR gauge is on the list. I have one but I have yet to get the bung welded on to fit the O2 sensor for it. Car has an aftermarket boost gauge and a 3” turbo-back exhaust with high flow cat. Also has Splitfire coil packs but I can’t see why that would affect anything (unless one had gone, but then that’d be a different set of symptoms?).
 
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When you say a pressure test..? Attach a vacuum gauge thing to one of the lines and see if it holds pressure when it’s pumped up?
 
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Basically you’re going to be checking the vac lines/boost pipes is holding pressure. Best thing to do is have a look over on SXOC this has been covered literally 1000’s of times with extensive write up and how to’s
 
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Basically you’re going to be checking the vac lines/boost pipes is holding pressure. Best thing to do is have a look over on SXOC this has been covered literally 1000’s of times with extensive write up and how to’s
Ok thanks, I’ll take a look on there
 
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Basically you’re going to be checking the vac lines/boost pipes is holding pressure. Best thing to do is have a look over on SXOC this has been covered literally 1000’s of times with extensive write up and how to’s
Had a quick read, that’s nice and simple to do actually - thanks for the heads up.
 
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I did a simple leak test today with soapy water (don’t have any compressed air system at home so couldn’t try that method) but that revealed nothing. I unplugged the MAF sensor and the car attempted to idle then died so it’s not that. I did the same with the TPS and it did idle but didn’t like being revved at all. Maybe the IACV is playing up after all, but it’s been properly cleaned out so I would have thought it would be ok.

I’m only about 2 miles from Horsham Developments so might take it in there and see if they can test it more thoroughly.






Silly old cars.
 
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Late to the story, but do you have an aftermarket BOV.. Also when you cleaned the IACV did you adjust the big nylon screw..
 
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Late to the story, but do you have an aftermarket BOV.. Also when you cleaned the IACV did you adjust the big nylon screw..
No, everything engine wise is completely standard (aside from the snorkel to the air box missing). Only difference is an aftermarket boost gauge.

I did take care not to touch that screw when I was cleaning the IACV. Maybe I did knock it or something, but the issue was no different afterwards to what it was like before I cleaned it.
 
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One thing I did a while ago was disconect the cold start on the throtle body, that made a difference to that high RPM on cold start and the drop in idle rpm..
 
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One thing I did a while ago was disconect the cold start on the throtle body, that made a difference to that high RPM on cold start and the drop in idle rpm..
Hmm, that sounds promising. Where is it exactly and what even is it? Is it some sort of weird 90s solenoid controlled system?
 
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Hmm, that sounds promising. Where is it exactly and what even is it? Is it some sort of weird 90s solenoid controlled system?
No, on the right hand side of the throttle body there is an adjusting screw for the cold start RPM...its easy to see...from memory I think you screw it in that way it stops it opening you butterfly valve...
 
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No, on the right hand side of the throttle body there is an adjusting screw for the cold start RPM...its easy to see...from memory I think you screw it in that way it stops it opening you butterfly valve...
Ahh right ok. I’ll give that a shot!
 
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That’s true actually. I’ll have to take it off and give it a service (if it’s possible). Thanks for the tips.
Very easy to do, and when you seperate it from the base you will see a small hole, block that up with a small screw, grind the head flat and thats your stock BOV mod which will hold upto 24psi of boost
 
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Very easy to do, and when you seperate it from the base you will see a small hole, block that up with a small screw, grind the head flat and thats your stock BOV mod which will hold upto 24psi of boost
Awesome, thanks man!
 
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No, on the right hand side of the throttle body there is an adjusting screw for the cold start RPM...its easy to see...from memory I think you screw it in that way it stops it opening you butterfly valve...


That little guy there?
 
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