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

[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.

[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

[ukkid35]

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

[ukkid35]

jammy_basturd said:

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

Hi James

Really sorry but my memory doesn't go back that far, however, I did everything you mention apart from replace the HT leads, and none of them seem to be the ultimate cause.

I can't honestly remember what the one crucial factor was, I even borrowed a flow meter from Peter Messling, but never got to use it.

I still have an idle well above 1000, but it doesn't runaway now, I've put that down to throttle shaft play.

I would check the state of the spriral throttle return springs, and fit one of Joolz long throttle return springs as well (assuming 4.5).

If I can think of anything else I will let you know, good luck.