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B21f idling high

Radtap

Well-known member
Joined
Dec 16, 2020
Location
Tucson, AZ
https://youtube.com/shorts/dPzOTS4PClo?feature=share
Got my 1980 B21f kjet finally running smoothly for the first time since previous owner parked it in 2000
Seems to be idling real high, adjusting the plastic screw on the throttle body doesn’t seem to have much of an effect, it’ll either do nothing and continue to idle high or the idle will significantly drop and borderline stall. What RPM should I be at and am I missing something?
I wanna say this thing still had 160psi in all 4 cyl and wasn’t locked up at all after 20 years, starts up on a dime and I am absolutely amazed. Only took an entire year to get to this point though
 
Make sure all the hoses are connected to where there supposed to be and that there are no vacuum leaks. You should also try pinching or plugging the hose to the brake booster.

An '80 would still have an auxiliary air valve and not an idle motor. It should have 12 volts across the terminals while the engine is running. It's a mechanical device with a bimetallic spring that slowly closes an orifice to lower the idle as it is warmed. The internal mechanism can fall apart so you may need a new one.

http://hiperformanceautoservice.com/images/AuxiliaryAirValveFunction.jpg
AuxiliaryAirValveFunction.jpg
 
Would there be any issue in just bypassing it? I'm in az so it's not like I need any cold start stuff and I can set my base idle a tad higher to compensate. Car will get up to 120 just sitting in the sun it'll probably open in seconds.
 
You will have to adjust the thumb screw so that it doesn't stall when cold but then the idle will be high when warm. Either that or hold the idle up manually until it's warm enough to idle on it's own.
 
It'll run, just not well. Some TBers have used ball valves from the piumbing department to act as idle air valves. Plumb it in place of the auxiliary air valve, and set it so the engine will run around 800-900 rpm. Another option is to use the idle adjustment screw for a 1983-89 LH-Jet 2.0, 2.1, or 2.2 car. Looks identical to the K-Jet assembly, but no holes for the aux. air valve hose or the vacuum line that goes to the AC idle boost circuit. Use that and plug off the nipple on the manifold. Set the idle around 900 rpm with the screw on it. It just won't have the 1500 rpm cold idle during winter.

Does the car have AC, btw? The AC idle boost solenoid could be energized at all times, if the AC switch isn't all the way off. Had an '81 with that setup on it. Whenever the AC switch was on, the idle would be around 2000 rpm. Off, it'd be at 850-900 rpm.
 
It does have ac, I remember turning it completely off to make sure that massive compressor doesn't kick on so I don't think thats it. I'll look into slapping a ball valve in there for the few cold winters we sometimes get, I have the idle adjustment for an lh car so I can give that a try too. I got it moving under its own power shortly after I took the video and drove it for a little and even after getting back home the idle didn't drop so I'm thinking that valve is bad, expensive part too. I plan on swapping a turbo b230 in about 6 months (hopefully), so not something I wanna buy, bypassed the fuel accumulator for the same reason.

I'll try and get a multimeter on the ac solenoid tomorrow to make sure that's not the problem.
 
Everything got religiously cleaned when I took it out to replace the fuel distributor. Only part I didn’t clean was the head intake runners, intake manifold, throttle body and air meter have all been cleaned. Gonna block off the auxiliary valve and try and start the car in a minute
 
Whoops, anyway got in the car today and the idle dropped lower without doing anything but still idling a tad high but now the screw finally works. I think that valve just had to work a bit, doesn’t seem stuck now and confirmed it isn’t the ac boost solenoid
 
Whoops sorry, I swear I put it in the right one but I guess not. Got my tach installed today so I can finally see where it’s idling, got it down to right around 800-900 rpm. Had a buddy bring a timing light and it’s sitting at 12 degrees btdc when according to the fender I should be at 8 +/-2 so gotta fix that but doubt that’s gonna cause any issues
 
That might be why it was idling higher than it should. 10 deg BTDC seems to be a happy spot for the B21F engines with Bosch ignition and K-Jet, like your car.
 
I'll try setting it around there tomorrow, had to return my buddy's timing light. also checked resistance on auxiliary air valve & reading within spec and its open when off so I think its alright. My dad informed me I had my throttle body setup wrong, I'm coming from carburetors so I thought that little stop screw was the idle adjust and set it so the butterfly was just ever so slightly open out of habit, bit of an idiot moment but that seemed to mostly fix my idle, actual idle screw still struggles a little to control it and have it almost completely shut to get it to drop low enough that I'm comfortable. Gonna adjust the timing tomorrow and see if it helps. Gonna also pickup a can of brake clean and check the intake manifold for leaks but the vacuum systems seems to be fine. Just gonna take some time and tinkering to dial it in
 
The solenoid the bumps the idle up for the a/c is counterintuitive, if you block the vacuum line to it, it will raise the idle, if you connect the 2 vacuum lines together it will lower the idle.
 
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