High Idle - temp related? Timing? (1 Viewer)

[Joshua993]

Hello all,

My 88 62 is still giving me a few fits. RIght now, as the engine warms the idle gradually increases. But when I run the A/C, the idle spikes instantly, and remains high even after the A/C is turned off. When I say high, I am talking in the 1100-1300 rpm range. Cranking down the idle screw does nothing to rememdy this.

I am not sure what to start troubleshooting on this. BSVS? I dont know exactly what it does, but I know it somehow affects the idle and timing advance through vacuum pressure - is that right?

Maybe the water temp sender? This is frustrating! Also, I am wondering about the factory timing setting - 8 Btdc. What is the baseline for this setting? What I mean is - what is the nominal or average altitude used to determine this? I live at 1330 ft ASL. Just wondering if I need to do some timing adjustment as well?

If you need me, I will be right here....

Thanks!

 

[RockDoc]

With the AC on it should idle at ~1000, ~650 with it off. When I had a high idle issue, it was related to the throttle position sensor being out of adjustment. Actually I had a high idle twice, the second time it turned out to be a broken wire to the idle speed control valve (the valve infront of the throttle body on the intake plenum). The FSM shows how to check both. There is no idle screw on a 62, the idle is controlled by the computer.

 

[Joshua993]

So, what is the flatblade screw above the TPS that I tweaked last night? Now I just feel silly! I am pulling the throttle body tonight for a good cleaning, and running ohms checks on the ICS and the TPS. Maybe i Wii find something off there....

 

[lcwizard]

With fuel injection a vacuum leak will cause high idle as the system adds fuel to correct the mixture.
Check vacuum hoses and plugs for leaks. While it's warming up the fuel injection is providing a rich
mixture which would mask a leak to some extent

 

[RockDoc]

It is sort of an idle control screw. It's an idle air bypass port, with the screw providing a crude adjustment of how much air is allowed past with the throttle plate close. At idle some air bleeds through this port and some through the idle speed control valve, with the computer fine tuning the idle by adjusting the ISC valve to get the amount of idle air correct. If everything is working right, there should be no need to adjust the screw (and no effect?). (of course I am working from memory without a throttle body sitting in front of me)

Perhaps you have a vacuum leak, as lcwizard suggests, or a throttle plate that isn't closing all the way, or an ISC valve that isn't functioning correctly, or the TPS out of ajustment so the computer doesn't know that it should be idling the engine (some folks have had the spring in the TPS get tired and stop returning the innards to the idle position).....

 

[Joshua993]

Hmmmm....so if all is functioning properly, there should be no change when turning that screw. It was definately adjusting the idle with minimal movement. Now I just need to isolate where the issue is.

I checked the TPS and ISC valve per the FSM this evening, with the exception of the bench test of the ISC - it got a little dark on me. So far, both have checked out fine. The ISC was fairly filthy - lots of stuf caked on it. I am not sure it had ever been removed since 1987-88, especially since I had to drill and easy out all three screws, even after squirting them with liquid wrench.

Tomorrow - a check of all the vacuum hoses. That shouldn't take too long...

Thanks for the replies guys. One just cant beat these forums for info and ideas!

J