Classic Idle fluctuates on V8 3.5L EFI

Hello, all. I'm having a problem with my petrol V8. The vehicle is a 1989 Range Rover Classic, with 3.5L EFI engine and 5-speed manual gearbox.

When started cold, everything is fine, but only for about two minutes. Once it warms up even the littlest bit, the idle starts fluctuating very regularly between zero and 1500 RPM. Just loping up and down, up and down. It's not erratic - it's very regular. "Ruh, ruh, ruh..."

When it's loping up and down, it seems like it smells rich when I'm standing behind it. Could the cold start injector cause this? If so, where is the cold start injector located, and can I just disconnect it? (I live in Spain, so it never gets THAT cold here.)

I hope it's not the air flow meter. They are pricey, I think...

Thank you in advance,

UPDATE: I found the cold start injector (right there, uhhh... in front of my nose) and disconnected it. No change. I also disconnected the air flow meter with the engine idling and the idle definitely changes. The loping up and down immediately stops and the idle just gets kind of ragged and random. So I suspect I have a problem with the air flow meter.

Before I buy one of these pricey little buggers, could it be anything else?

Idle air control valve?

+1 on the AIV (stepper motor) at the rear of the plenum. Could be sticking or dirty.

Also is it the hotwire or flapper airflow meter? If the former it can be - carefully - cleaned.

It's the flapper-type meter. The AIV is at the back of the plenum? Near the bulkhead, or on the same side as the 9th injector?

Try cleaning round the butterfly valve...

Pete The Biker said:

Try cleaning round the butterfly valve...

Click to expand...

Dude, you may be a genius. I sprayed it down with WD40 and scrubbed it out with a toothbrush and now it seems to idle perfectly. The only problem? I called to brag to my friend and he said: "You cleaned it with WHAT? Don't spray WD40 into a throttle butterfly. It will queer the electronics."

I still don't have any idea if it's really fixed, but I will test it this evening and tomorrow and see if I can get it to act up again...

Fingers crossed!

Congrats. on (hopefully) curing the problem.
Two points for future reference:
There is no stepper-motor on the 3.5efi - unless the late model with the hotwire system had one, but certainly not with the 'flapper' system.
Even here in the UK I've always disconnected the C/S injector, never needed it even in mid-winter.

norseman said:

Congrats. on (hopefully) curing the problem.
Two points for future reference:
There is no stepper-motor on the 3.5efi - unless the late model with the hotwire system had one, but certainly not with the 'flapper' system.
Even here in the UK I've always disconnected the C/S injector, never needed it even in mid-winter.

Click to expand...

Thank you! I'm glad I'm not going crazy, because I looked and couldn't see anything on the back of the plenum that looked like what I picture an idle air control looking like.

I'll keep testing and post when I know whether it seems to be fixed or not.

norseman said:

Congrats. on (hopefully) curing the problem.
Two points for future reference:
There is no stepper-motor on the 3.5efi - unless the late model with the hotwire system had one, but certainly not with the 'flapper' system.
Even here in the UK I've always disconnected the C/S injector, never needed it even in mid-winter.

Click to expand...

Sensh said:

Thank you! I'm glad I'm not going crazy, because I looked and couldn't see anything on the back of the plenum that looked like what I picture an idle air control looking like.

I'll keep testing and post when I know whether it seems to be fixed or not.

Click to expand...

There is an idle air control valve on the 3.5EFi but as you say it is not a stepper motor on the side of the plenum...it is a bimetal strip in a housing usually bolted to the top of the intake manifold behind the plenum....when the bimetal strip warms up it closes the bypass air and acts like an automatic choke....

Saint.V8 said:

There is an idle air control valve on the 3.5EFi but as you say it is not a stepper motor on the side of the plenum...it is a bimetal strip in a housing usually bolted to the top of the intake manifold behind the plenum....when the bimetal strip warms up it closes the bypass air and acts like an automatic choke....

Click to expand...

Thanks again. Do you by any chance have a photo of what the part looks like? Or a listing on Paddock Spares or something? That would help me, and my searches are turning up nothing.

I have spent the better part of two days driving the RRC as much as possible, and since cleaning the butterfly it hasn't acted up once. The engine fires up easily, idles like a rock at around 650 rpm, and drive wonderfully. It even fully smoother at light throttle, light load, like when trundling through traffic.

Thanks to all. I think I can cautiously say that fixed it.

Result - well done!

Glad it worked for you! Well done!

Pete

Sensh said:

Thanks again. Do you by any chance have a photo of what the part looks like? Or a listing on Paddock Spares or something? That would help me, and my searches are turning up nothing.

Click to expand...

Located in front of plenum, my bad....here are some images...part number ERC3617

Very, very helpful, thank you!!