Engine Issue #1 - High Idle

[ukkid35]

Although the recently (top end) rebuilt AJP8 4.5 runs, it has a few issues. The first and most awkward is the high idle. This seems to vary from about 1200 when cold, to 1800 when hot. This makes it near impossible to drive in traffic as the ECU temp climbs higher and higher reaching 98 on the trip back from Brands.

Is there anything that could cause the high idle other than false air? The throttle pots read 18% when idling, they read 14.8% when fully closed.

The reason I suspect air leaks is because the only way I could fit the fuel rail after the head skim, was to fit the fuel rail first, and then torque down the intake manifold. I didn't use new O rings on the intake insulator, so that is probably the obvious option, but is there anything else I should try?

TIA

[JensenA]

After your amazing 'project' and all the effort you put into it, I think you deserve all the help we can give you Paul. So here's a couple of suggestions, I hope many others who are more knowledgeable follow....

It does sound like an 'air leak' issue, but check that the Air sensor on the front air intake (On the passenger side) is connected, and as aprecaution try re-bleeding the cooling system again.

[Tanguero]

Does it run at all with the idle screw backed right off and throttles fully closed? If so at what RPM?

[pmessling]

From reading your other post and recent experience I would start with the basics. Sync flow each bank and TP and adjust the idle screw. Do it when the engine is hot so every things at its maximum expansion. How old are you TP. Mine currently idles all over the place sometimes about 1500 up to 1400. So will be doing mine soon but when I last changed my lambda the adaptive maps were not within tolerance even when moving them with the computer plugged in. So I'm changing them soon and starting again to get it right.

[Ron Fellows]

Idle screw and throttle cable possibly sticking may also be the issue.

I had this when the cable was wearing slightly. If the pots read what they should and its balanced just check this.

Physically put your foot under the pedal and pull it backwards and see if any changes.

[julian64]

I tend to start the old fashioned way by disconnecting all the throttle linkages, winding all the throttle stops back and making sure I can stall the engine with the butterflies closed.

If I can't I go along each inlet and put a hand over it till I find the one thats leaking. If a hand can't stall it then I'll go to the head bolts/gasket.

[ukkid35]

julian64 said:

I tend to start the old fashioned way by disconnecting all the throttle linkages, winding all the throttle stops back and making sure I can stall the engine with the butterflies closed.

If I can't I go along each inlet and put a hand over it till I find the one thats leaking. If a hand can't stall it then I'll go to the head bolts/gasket.

Sounds like a plan - many thanks.

[ukkid35]

Tanguero said:

Does it run at all with the idle screw backed right off and throttles fully closed? If so at what RPM?

Yes, it runs at 1050-1100, can't stall it at all. TBH I can put up with that for now, but long term do I need new butterflies.

It was interesting watching it run without the purple hoses, seeing the fuel wash over the butterflies, and then seeing it ignite once with a small bang... Scary stuff, especially since I can see that my car has already suffered an injector fire of some sort in the past.

[Tanguero]

ukkid35 said:

Yes, it runs at 1050-1100, can't stall it at all. TBH I can put up with that for now, but long term do I need new butterflies.

It was interesting watching it run without the purple hoses, seeing the fuel wash over the butterflies, and then seeing it ignite once with a small bang... Scary stuff, especially since I can see that my car has already suffered an injector fire of some sort in the past.

That is way too high! It shouldn't run at all if the butterflies are closing properly. I would disconnect everything throttle related and check carefully that both banks butterflies are closing properly. I think the correct gap for a feeler gauge under the edge of the butterfly is in the engine section of the WSM . If they are closing, then you have a reasonably substantial air leak elsewhere. The most likely place is from missing or badly seated 'O' rings on the throttle heat barrier, but it could also possibly be injector 'O' rings.

When you are fitting the heat barrier, use a tiny smear of grease to hold the bottom 'O' rings in the grooves. I have found that reusing the old 'O' rings doesn't tend to work too well as they will have flattened and stretched.

The engine should not run at all with the idle backed right off, so it is definitely getting air from somewhere.

[ridds]

ukkid35 said:

Tanguero said:

Does it run at all with the idle screw backed right off and throttles fully closed? If so at what RPM?

Yes, it runs at 1050-1100, can't stall it at all. TBH I can put up with that for now, but long term do I need new butterflies.

It was interesting watching it run without the purple hoses, seeing the fuel wash over the butterflies, and then seeing it ignite once with a small bang... Scary stuff, especially since I can see that my car has already suffered an injector fire of some sort in the past.

In the intake???? You shouldn't be seeing any sort of bang. This would add to the suspect cam timing giving you reduced power.

[ukkid35]

There must be different throttle stops that I haven’t found, presumably there is one on each intake manifold somewhere, rather than just the main idle adjustment near the cable.

There are no air leaks around the insulator, even though that was my main suspicion. I went to the expense of fitting 16 new O rings (£25 from RaceTech) on Saturday, but the old ones were fine, and hadn’t been trapped or damaged by the way that I have had to fit the fuel rail – tightening up the intake manifold bolts after fitting the fuel rail. Injector O rings can’t be the problem as they are upstream of the butterflies, which seems very weird.

Edited by ukkid35 on Monday 7th November 12:42

[Tanguero]

Backfiring in the intake really does sound like a cam timing issue.

I can't help with the location of the throttle stop on a 4.5 manifold (also explains why the injectors are upstream from the butterflies - unlike a 4.2), but I am sure someone with a 4.5 will be along shortly.

[pmessling]

There is only the one stop on the drivers side back, the passenger bank is adjusted using the link rod to open or close the butterflies to adjust the idle.

[Rufus Roughcut]

I struggled to get my tick over below 1200rpm, it was pretty obvious what was wrong once I'd taken off the purple hoses.





.... after replacing the O rings and heat barrier the tick over was still >1000rpm with the link disconnected and the stop backed off.

If you look at the photo below you'll see there is a hollow casting between the bodies where the emissions pipe connects to, the bleed holes are bypassing the butterfly! try clamping the pipework??

Edited by Rufus Roughcut on Monday 7th November 13:49

[Nickccc]

When I looked at your last picture I thought you had put the tie wrap on to stop the gasket falling off, but it's with the throttle bodies on the car, can that clamp down properly like that? Or is there a recess it sits into?

[Rufus Roughcut]

Nickccc said:

When I looked at your last picture I thought you had put the tie wrap on to stop the gasket falling off, but it's with the throttle bodies on the car, can that clamp down properly like that? Or is there a recess it sits into?

Yes, plenty of space, from memory there is approx 30mm of clearance under the heat barrier.

Yes you are correct I could have removed the tie wrap, however it's doing no harm and probably help if the throttle bodies need removing in the future.

[Nickccc]

Ok, it's been a while since I had to pull the TB's off which is a good thing.
I don't suppose anyone has a picture of the area the TB's connect down to.
I had the high idle thing after one of the bodge rebuilds, the TB's had been cracked somehow during refitting, would idle even with the screws backed right out needed to be welded to sort them out.
As others have said you have air getting in from somewhere for certain.

[FarmyardPants]

Maybe you could pull in injector plugs one at a time to see which (or which bank) causes it to stall?

[ukkid35]

Hand over each throttle body showed they were all pulling a strong vacuum.

[jammy_basturd]

Did you ever find out what was the cause of this Paul?

I have similar symptoms. Started the car up this evening after a couple of months of being laid up - note that I had the same idle issues before being laid up. Starts up, idles at about 1100rpm. After 20 seconds the engine just dies, doesn't slowly die, just dies in about 1 second. I figure the engine is cold, started it up again and went out for a drive. Drove fine. Got back, idling about 1500-1600rpm. Steady idle though.

Work I have recently done after an extended period of being laid up:

• New rose joints on the throttle linkage.
• New o-rings on the thermal barrier when I last fitted the inlets.
• Engine setup procedure in the engine manual followed exactly.
• New spark plugs and HT leads

Couple of other things to bear in mind. I seem to remember, when I had the car running a few months back, that it bogged down a bit when I tried to accelerate quickly. On a cold night like tonight it wasn't so bad - so maybe over fueling? The other thing is that I had a bit of trouble that was ultimately traced to a bit of damp on some of the ECU connectors - which has now been rectified.