240 b21ft CIS High Idle

1983 245 turbo m46


Trying to figure out a sudden high idle issue.


The car was perfectly happy, idling at around 900-1050rpm. Then, fuse #13 blew the other day when I was driving, and the car immediately shut off. Stupidly without extras in the car, I replaced it with the fuse from fuse #1, and the car started and idled /chugged at ~500rpm.

I did all of the electrical tests in the Bentley. Pin #5 was showing nothing. I took everything apart, and realized that pin #5 had come loose from the plug. I snapped everything back together, and since I had a replacement IAC from @john242ti, I threw that in there as well. I tested the IAC before installing it, and I was getting ~12 ohms between 3-4 and 4-5. Just for kicks, I tested the original IAC and got practically the same result.

Now that I have the car together, it's now idling at 900 on cold start, but as the car warms up, the idle raises to around 1500-1800rpms.


Questions:

1) Am I missing something here? Everything in the Bentley is based on having too low of an idle--not too high. I am quite sure there are no loose vacuum lines since it was just fine before.

2) The Bentley calls for "approximately 20 ohms" on the IAC valve. Is the 12 ohms I'm seeing good enough?

3) I read that the CIS ECU can get "burned" if there is a short in the system. Could this be my problem? How does the ECU come apart? I can't seem to get it open.

4) Is there a way to test the ECU?

5) Anyone have a turbo ECU lying around?


**For posterity, this happened on the first drive after I replaced the brake junction block and bled the brakes. Everything is 100% in the brake system now, so I can't imagine this has had an effect, but...

Thanks in advance!

Throttle switch adjusted ok?

Want to bring it out Saturday and we'll get it set up how mine is?

Make sure the idle switch is working as John mentions. Also be sure the coil connection is good as well. If the system doesn't see the correct rpms or idle switch position. It can keep the idle air motor open and raise the idle higher. Another possible reason is the coolant temp sensor is bad or has bad connections to the controller. That is how it knows to raise the idle for a cold engine.

Yes, if the idle motor causes a blown fuse the idle control box can fail. I've never had that happen but have read claims of that happening. In the bentley there are a few tests and if they pass then the controller box is probably bad.

That fuse from #1 was an 8-amp fuse like #13, wasn't it? If it was a bigger one I'd check to see if the foil in the idle controller might have opened instead. Root cause, I'd think is the old insulation problem you can see in my photo -- this not being the usually already-replaced engine harness, but the link from the firewall into the idle controller. A short can destroy one of the idle air valve driver transistors.

How do you open the box? Obviously I wasn't patient enough, and I thought I was pretty good at getting snap-fit electronics housings apart so they can be put back together. Oops.

Such fantastic info from everyone. Much appreciated!

After going back through the tests again, I did find that the throttle switch was allowing continuity at idle if the throttle was barely opened and then left to shut again. Reset that. The car was still idling high, so I grounded the CIS system through the test port and turned the throttle screw until it was back to 850-900 rpm. After opening the circuit, everything is a-ok.

The car does get a bit of a lopey idle in between full cold and full warm. I suppose I need to look at fuel pressures again?

I had a mechanic look at the car a year or so ago when I could not be near it and wanted it shipped out west. I remember him saying something about the IAC controller. Maybe he had turned the screw when he couldn't find the unplugged pin?

That said, I'm still confused about the timeline. How could the car be running at a decent idle before the fuse blew, super low idle with the fuse replaced, and then high idle with the pin snapped back into place? I mean, if the pin was detached before the fuse blew, the idle would have been low then, too, right? If it wasn't detached before the fuse blew, then the idle should have been high, right? Something isn't matching up here.

I will look closer at the firewall connection, but I'm pretty sure all is good there. And yes, that blown fuse was an 8 amp.

Dp'd

How does this fuel system control a/c idle up? I know my regular B21F k jet had a solenoid mounted on the firewall that operated a vacuum switched air valve. It worked in reverse of a "normal" solenoid since it was normally open and passing air until energized. I had the hose from the vacuum operated valve split one time as well and cause a high idle

Constant idle when combined with Bosch breakerless just maintains the normal idle rpm. With Chrysler, it'll bump up from 750 rpm to 900 rpm on 1982 models (and, LH-Jet cars do the same). 1981 models would just maintain normal idle. Non-constant idle K-Jet cars, like yours, and my old '81 after I installed a B23E, have that solenoid on the firewall and the plastic valve in the "L" shaped hose coming from the adjustment screw that goes to the bottom of the AAV. When the AC switch is turned on, the idle goes from 900 to around 2000 rpm.

Amazing detail, as always, John. Can’t fathom how you remember all of those bits and pieces.

Day 2 of decent driving. Still lopey in the warm up, but I haven’t had time to mess with it. Through text, John explained that lopey idle would be the O2 sensor kicking in. I’ll start looking through the Bentley and see if I can figure out how to deal with that.

The timeline of my IAC woes is still a bit of a mystery though. Hopefully I’ll goof around enough in the engine bay to discover something.

It takes a bit longer for the single wire sensor to come up to temp. So a bit of an idle that hunts is normal on the B21FT with CIS. it's kind of why Volvo came out with the 123 control pressure regulator to keep the engine in warmup just a bit longer.

dl242gt said:

It takes a bit longer for the single wire sensor to come up to temp. So a bit of an idle that hunts is normal on the B21FT with CIS. it's kind of why Volvo came out with the 123 control pressure regulator to keep the engine in warmup just a bit longer.

Click to expand...

It's not that it hunts. The tach needle is dead even, but the car shakes. Once up to temp, the needle is in the exact same spot, but the engine is smooth. Maybe the tach needle just doesn't have that fine of a calibration. I'll have to hook up my old dwell/tach meter to check it out if I can remember how. Hilariously, I replaced an 079 CPR with a 123 a couple months ago.

I gotcha. That is a bit different. My tach was moving with the changing engine rpm. Might just be the difference between a open loop not quite warmed up idle vs closed loop hot o2 sensor idle. maybe a worn engine mount is also showing up with it cold idling?

For the short time it lasted I like how he 123 regulator had the longer warmup. Now my car has an 079 in it again.

Popped fuse #13 again tonight. Put in a new one right away, and it's doing just fine.

I rewired the fuel pump relay connection a while back. Could I have a short in the between them causing it to eat fuses?

Try to get the copper and brass fuses. They last a bit longer.

Got stuck in a Lowe’s parking lot for a bit this evening.

#13 blows
shut off car
replace #13
start car
repeat

after the fifth fuse, it finally decided it was going to take me home. Drove fine.

I dunno what is up now. Where would there be something getting grounded in the system?

Check the wire to the A/C compressor.

hiperfauto said:

Check the wire to the A/C compressor.

Click to expand...

Just looking this up via the wiring diagrams is making me want to

Hopefully this will do the trick.

I had a similar problem with my '83 DL after I installed a new engine and left the compressor disconnected. The wire would randomly ground and blow the fuse which would kill the engine.

hiperfauto said:

I had a similar problem with my '83 DL after I installed a new engine and left the compressor disconnected. The wire would randomly ground and blow the fuse which would kill the engine.

Click to expand...

I did too. 83 DL. In that year, the LH fuel system used the same fuse (12) as the AC. Next year they moved the fuel system fuse to 13 where it always was. The AC is on 12 and fuel system/idle controller on fuse 13 in the 83 k-jet turbo.

Thread conclusion

After cleaning an enormous amount of contacts and the fuse continuing to blow, I finally realized it was blowing every time I used the left signal. One of the wires of the left front corner marker had been mashed between the quarter panel and the light itself and had worn the sheathing away over time--creating a ground.

Crazy to realize that a grounded wire to a turn signal will stop the car dead in its tracks.

Also, there is no pin 7 to the CIS unit on a turbo car.

Thanks to everyone who helped!

/thread