Noz1974

Hi everyone!!
So I've just rebuild my car and got her running but I've got a niggle with the idle.
So if the car is sat idling at 800rpm, cold or hot and I Rev the engine, as the needle comes back down it goes really low to like 400 rpm almost cuts out then recovers to 800 and begins to idle properly again, it's as though the idle is too low on the throttle body( cable type) but it looks like it is factory set with no means to adjust the grub screw which the throttle mech sits on at idle.
I'm thinking it's probably the MAF or oxygen sensors on the cats, I've checked the crankcase vacuum which seems ok, if you take the oil cap off you can hear the idle change and its sucking air in which is what it should do I'm told!!
Anyone had this ???

DBJoe996

Before you do anything else, you need to check the Idle Control Valve on the throttle body. You may need to remove the throttle body and remove the ICV, then clean it out. Clean the throttle body as well. Reinstall everything and see if things work right. Could be a bad ICV as well. Normally, a faulty MAF and/or O2 sensors will throw a CEL and produce codes. Any CEL and codes?

Noz1974

Hi DB , no codes had it up to my porsche indie who has been helping me here and there and they had it on the computer but no codes so might be what you said, I cleaned the throttle body itself with a bit of carb cleaner but didn't take off the control valve, idthere a gasket to replace when you put it back??

Ahsai

Also activate the ICV with a 9V battery when you're cleaning it. Will help loosen up the crud.

Noz1974

Ahsai
Do you think it will be the ICV from what I've said??
What should I clean it with, switch cleaner??
Is there a set way to connect the battery and should I see something move or open??

Ahsai

When the engine is hunting idle, the usual suspects are throttle body, ICV and intake vacuum leak. Also, the ICV is known to cause idle issues for your model so may as well clean that first.

Supply positive 9-12v to pin 2, then negative to either pin 1 or 3 (not at the same time) and the valve will rotate in different directions.

Have you checked the O2 sensor voltage and see the car is indeed in close-loop fuel control? MAF should read 1.3v @ warm idle.

Noz1974

Ahsai
No I haven't checked that closed loop control, please can you explain how I do this too, I'm going to clean the idle valve today!

Ahsai

Do you have Durametric or a generic OBDII scanner that reads sensor values in real-time? One of the items it reports is called "Close loop fuel control" yes/no.

You need those scanners to check MAF and O2 reading as well.

Noz1974

Unfortunately I don't have anything to read the codes I'll have to go with the clean then take it up to my indie if it still continues after that, what's the best one to get for the money ??

Ahsai

If you use Android devices, the best bang for the buck is the $10-20 bluetooth OBDII reader and the $5 Torque Pro app. If you use Apple devices, you can get the WiFi OBDII reader (more expensive) and get the #$10 OBD Fusion app.

To diagnose any engine problems, you need at least the above and ideally Durametric.

Noz1974

Ahsai
Was the ICV it was jammed solid!! Blasted it with penetrating oil then cleaned it out with carb cleaner, had to move it with the tip of a screwdriver to get it going it was so tightly stuck, got it moving then tried battery but it was still too tight , had to keep moving it manually ( I was very careful) and spraying more penetrating fluid it, eventually I got it so it was literally flicking open and closed so freely when I put the battery on.
Put it all back together and she's loads better
Thank you 👍👍👍👍👍👍👍👍

Noz1974

Sorry thanks also to db joe !!

Ahsai

Well done! Yes, Joe nailed this one.

Noz1974

Thanks , I'm good on mechanical, but need to start learning all the electronic side of things, think I need to be investing in a durametric soon!