Low idle, hesitation

[6o4turbo]

So I've had my car off the road for 7 months, in that time I have replaced many things, and done a lot of work on it. Recently installed a new, bigger turbo as well.

The car fires up fine, starts to idle around 800 RPM, then as it heats up, a minute or so later, the idle drops to 500 RPM, and struggles to keep running.

There is a LOT of hesitation on when on the throttle, it stumbles and hesititates severly.

Vac. is at 10 hg at 500 RPM

4000 K on a new, built motor.

I'm thinking possibly TPS or ISC? Spark plugs?

Some input would be greatly appreciated,

Thanks,

- Kev

 

[jetjock]

10 hg? Not good...

 

[6o4turbo]

I'm aware of that.

 

[6o4turbo]

Is it that time of the month for you or something? Damn.

 

[jetjock]

Ok, maybe I misunderstood. Are you offering up the 10 hg as merely a symptom or are you saying you know it's not right but can't find out why it's low? You must feel it doesn't have any bearing on the problem or you wouldn't have asked about plugs, ISC, and the TPS. In other words why haven't you found and repaired the cause of the low vacuum? Why would you expect the engine not to have the symptoms it does with 10 hg?

 

[6o4turbo]

I went through all the vac lines I know of, and couldn't find a leak. Where else/what ese would you reccomend checking?

I was under the impression that low vac would result in high idle, not low. Is that not the case?

Last year it made 21 at idle.

Thanks.

 

[jetjock]

Pirate air, bad compression, valve lash, valve leaks, or timing, restricted exhaust, ignition timing, bad brake booster, HG, could be lots of things. Is the reading steady low or pulsating? What is vacuum off idle, say at 2500 rpm? What is cranking vacuum with the EFI fuse pulled? Sounds like a leak or valve timing to me. What work did you do?

 

[Nick M]

When the engine is cold, the mixture is much richer, because it is easier to light. But as the engine warms, the ECU leans it out to a different mixture. If you have a mechanical problem, such as that 10", you need to stay rich to light off.

I think JJ is looking at the right thing.

 

[6o4turbo]

Pirate air, bad compression, valve lash, valve leaks, or timing, restricted exhaust, ignition timing, bad brake booster, HG, could be lots of things. Is the reading steady low or pulsating? What is vacuum off idle, say at 2500 rpm? What is cranking vacuum with the EFI fuse pulled? Sounds like a leak or valve timing to me. What work did you do?

Vac is steady at 11 inHg to be exact.

I'll check with the EFI fuse and 2500 RPM vac within the hour.

Mechanically, new turbo, new air filter, valve cover gaskets (cleaned out the oil in the spark plug valley as well) front main crank seal, timing belt, timing belt tensioner, alternator, battery. Is all that is coming to mind right now...

I don't see how it could be valve timing, as it was never touched and was fine before.

Could a small leak an IC pip cause the loss of 10 inHg?

Thanks.

 

[6o4turbo]

When the engine is cold, the mixture is much richer, because it is easier to light. But as the engine warms, the ECU leans it out to a different mixture. If you have a mechanical problem, such as that 10", you need to stay rich to light off.

I think JJ is looking at the right thing.

I am also getting high EGT's.

Throwing a code 51. Could that be related?

Went over every coupler/clamp, couldn't find a boost leak.

 

[jdub]

Vac is steady at 11 inHg to be exact.

That is low...could be for any of the reasons above.

I don't see how it could be valve timing, as it was never touched and was fine before.

Unless you jumped a tooth...if it was re-built, did you re-tension the timing belt after 500 miles or so? Check your timing.

And fix the code 51.

 

[6o4turbo]

That is low...could be for any of the reasons above.



Unless you jumped a tooth...if it was re-built, did you re-tension the timing belt after 500 miles or so? Check your timing.

And fix the code 51.

Just replaced the timing belt tensioner, and timing belt, only have 30 Kilometers on them so far. So it might just be that the belt is off a tooth? Makes sense, as the car had better vac. before the timing belt change.

 

[jetjock]

I don't see how it could be valve timing, as it was never touched and was fine before.

Just replaced the timing belt tensioner, and timing belt, only have 30 Kilometers on them so far. So it might just be that the belt is off a tooth? Makes sense, as the car had better vac before the timing belt change.

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