Irratic Idling

[jsc1976]

Can anybody help?

Before anyone comments stepper motor is spotless!

I have a 4.0 Chimaera which seems to suffer from an erratic idling problem. Once driving all is fine and it pulls and sounds as it should. When idling though it tends to be all over the shop. Initially when throttling off it would tickover at anything up to 2k or rise and fall from 900 to 2k. It was then serviced and new plugs, leads and supressor caps were put on. This made no difference but the guys who serviced it suggested there may be an air leak somewhere around the inlet manifold.

I had a tinker myself and adjusted the idle screw on the plenum chamber (as the bible suggests), this made things a lot better but it still idled at anything from 600 to 1300 and occasionally stalled. I had a further tinker today and removed the stepper motor connector once the idle had settled and it seemed to cure the problem (idled perfectly at about 900rpm). Now I would assume this would point to a faulty stepper motor but looking back through the cars history this has been replaced a couple of times already. Can anybody suggest anything. The only other thing I have noticed is that the temp guage does not get above 70 degrees and at this point the fans come on. Could the temperature sender be faulty (I have read previously these can cause idling problems) or are there different senders sending info to the ecu and the guage?

Any help would be appreciated even if it simply confirms the service guy is likely to be right with the air leak.

Many thanks

Jody

[greenv8s]

Disconnecting the stepper motor is a good first move, amongst other things you're eliminated air leaks and a whole host of sensor/tuning problems. In fact leaving it disconnected permanently is a viable solution. When you adjusted the base idle, did you set it properly? To do this you need to block off the air bypass hose to the stepper motor housing, and then adjust the base idle screw until the engine idles at about 500 rpm. The engine may not be happy to idle this low so a good way to do this is to squash the air bypass hose under your thumb, you can ease off to pick the revs up and keep the engine running if it starts to falter while you adjust the base idle screw. Once you have set the base idle the stepper motor will be around the middle of its travel at dle which minimises the risk of it hitting the end stops, jamming, overshooting etc. On the other hand, as you've probably found, the car runs pretty well with the stepper motor unplugged and it avoids a whole heap of problems.

[jsc1976]

Thanks GreenV8s,

I will have a go at setting the base idle as you have described. Excuse my ignorance but I take it from your comments that the symptoms suggest a stepper / base idle problem and not an air leak?

[Mike Heynes]

Try cleaning the gunge from around the throttle butterfly - It's worked for me twice and I've had a Chimaera for 6 years now - it seems to be a very common problem.

Mike

[2 sMoKiN bArReLs]

I gave up worrying about erratic idling, it just seems to be one of those things.

[jsc1976]

Thanks Mike,

How do I get to that? Is it a case of removing the air intake pipe from plenum to air flow meter or do you remove the throttle pot?

Thanks

[Mad Mitch]

2SB.... Good advice given. You can take two approaches to TVR ownership. You can worry about every little minor problem and spend heaps of time/cash sorting them, or you can establish that no major problem will come of them and just keep it safe and drive the bugger. Since i stopped worrying about every little noise or strange "moment" i enjoy the driving experience every time we go out.My oppinion only of course

[2 sMoKiN bArReLs]

Mad Mitch said:

2SB.... Good advice given. You can take two approaches to TVR ownership. You can worry about every little minor problem and spend heaps of time/cash sorting them, or you can establish that no major problem will come of them and just keep it safe and drive the bugger. Since i stopped worrying about every little noise or strange "moment" i enjoy the driving experience every time we go out.My oppinion only of course

[Tobs]

I had a similar problem on Monday - when stopping at light etc - idle would wander up to 1500rmp then down to 500 then the engine would stall. After poking around the engine for 5 minutes in my works car park (I'm sure this causes amusement to other people who work here - "look the TVR's bonnet is up again!" I discovered that I had forgotten to tighten the hose clip on the pipe from the airflow meter to the plenum when I was working on it at the weekend

Toby.

[DamnWiseguy]

Clean the contacts on the temperature sender, worked for me.