LH2.4 Periodic high idle until restart

Heyo Brick Peeps!

Got an annoying problem that I can't figure out for the life of me... About 50% of the time when I'm out and about running errands I'll get into the car, drive off and notice a high idle around 1,000 rpms at the next red light. I'll turn off the car and start it back up to have a nice solid idle at 750 rpms for the rest of the drive. ECU and EZK only show 1-1-1

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About the car - 1991 740 b230ft + 16v
984 ECU and Gold box EZK with Hituning chips
3" MAF
Delphi 42lbs injectors
do88 Intercooler and no leaks between the air filter and the tailpipe
Rebuild turbo
Rebuilt motor with new pistons, valves, etc. with ca 3,000 Miles on it
Spark plugs Bosch WR5DC+
Red Top battery about 5 years old
80A Alternator and charging system good with a solid ~14v at idle

Preventative maintenance:
All harness grounds renewed/new connectors
ECU and EZK pin voltages/signal/ohms checked between boxes and sensors/actuators (that includes voltages at the MAF and Idle control valve as well as the TPS open/close signal)
Firewall bulk connectors removed and wires soldered and heatshrinked
Relay/fuse panel removed and all crusty or suspicious wires/connectors replaced
Relays checked - all good

And the following things have been done:

NEW Bosch parts, not junkyard or refurbs
Coolant temp
Crank position
Idle control
O2
012 MAF
Fuel Filter
Fuel pressure regulator
110 Porsche CBV

Other goodies
New Deatschworks DW200 Fuel pump
All fuel lines replaced
All vaccum lines replaced
New oil seperator box
Fuel tank cap like new

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As far as the weather is concerned, don't matter if rain or shine, cold or hot. When the motor is warm it's a 50/50 chance it'll idle high till restart then be fine for the rest of the trip. So help me out ya'll! What is going on here?

You don't mention the TPS. Edit: I see you did measure the voltage. A click doesn't confirm it is closing at closed throttle, especially if it is set at the hairy edge or has been exposed to blow by oil. The IAC control memorizes the valve opening at its last successful idling and keeps that pulse width during open throttle -- until you shut it down and start over.

Hang an LED test lamp on the TPS closed throttle lead (ECU 2 or EZK 7) and watch it for consistently going out when you release the throttle.

Hi Art,

Thanks for the suggestion!

But I have already checked the TPS open/close signal at the ECU, used the LH2.4 diagnostic function just for kicks, checked adjustment to not click with a 0.45mm feeler gauge, but to click with a 0.15mm feeler gauge and even swapped the thing with a known good unit from my second 740 with the b234f motor.

JerryJS8 said:

Hi Art,

Thanks for the suggestion!

But I have already checked the TPS open/close signal at the ECU, used the LH2.4 diagnostic function just for kicks, checked adjustment to not click with a 0.45mm feeler gauge, but to click with a 0.15mm feeler gauge and even swapped the thing with a known good unit from my second 740 with the b234f motor.

Click to expand...

OK, sounds like you considered this case where the switch is dirty. I jumped on it because I had a similar issue I didn't find until I hung a scope on the lead and watched the noisy make of the Microswitch contacts about every third time I tapped the accelerator pedal. Now I have a breakout tool to monitor it from under the hood using an LED.

Aside from the TPS the symptom also reminds one of the missing wheel speed signal which normally sets the 311 on ECUs not running modified firmware, especially the part where you need to shut down to restore idle control. I discounted this as you say the DTS isn't recorded.

Good luck in your pursuit. We both stand to learn something.

Sounds like what I experienced with the VSS signal disconnected - http://forums.turbobricks.com/showthread.php?p=5954896#post5954896

I forget if the 3-1-1 code showed up after turning the engine off and on, or if it only showed up when idle was high, before turning the engine off.

Are your speedometer and odometer working correctly? (VSS comes from the speedometer circuit board to the LH2.4 ECU)

I haven't found the key to that one yet but I know several others dealing with it, and I have dealt with it as well. In my case, changing the EZK back to a stock tune made the issue go away, leading me to believe it's something in the tune. My current tune doesn't have the issue either.

Ezk and ecu do not recieve your speed from the rear axle

cleanflametrap said:

Aside from the TPS the symptom also reminds one of the missing wheel speed signal which normally sets the 311 on ECUs not running modified firmware, especially the part where you need to shut down to restore idle control.

Click to expand...

bobxyz said:

Sounds like what I experienced with the VSS signal disconnected

Click to expand...

Naciremus said:

Ezk and ecu do not recieve your speed from the rear axle

Click to expand...

Three votes for VSS, sounds like that's my next place to search. My speedometer and odometer work perfectly, so I'll look into the wiring from the odometer to pin 34 on the ECU.

@gsellstr - I'll see if swapping the EZK makes a difference if the signal wire ain't the problem.

Thanks for your help guys, I'll keep you updated!!!

I had a similar issue where when warm, it might or might not creep up to about 1000 rpm. Reset the TPS to factory specs (sounds like exactly as you did) and still did it. Took off the throttle body, cleaned it, reset the blade. Reinstalled throttle body, set it to spec, installed TPS, set THAT to spec, all better. My kid's 940 Turbo had the throttle blade WAY out of whack which caused all kinds of shenanigans. You might want to check it out. With the base idle screw backed way off, loosen the two screws holding the throttle blade in place just a little, maybe quarter to half turn, just enough so that you can move the throttle blade but not so much that it flops around. DON'T TAKE THEM OUT. Adjust blade so that you see a minimum of light through the throttle bore, I doubt you'll get it to seat completely, but it should be damn close. Tighten screws, reset base settings.

No VSS signal holds code 3-1-1 and bumps idle to like 1700. Had that too.

If you can trust your idle valve doesn't have any sticky places, monitoring the duty cycle inside the car can offer a clue to whether the anomalous extra air is being added by the ECU or otherwise, such as past the throttle. One of my old multimeters has duty cycle/frequency function. It would provide an instant proof at a glance if left on the passenger seat during a test drive.

Testing with a 951 I found the control range to be 25% to 62%.

Something not commonly mentioned is regardless of idle motor, LH can still play with idle speed. The EZK will adjust timing at idle based on certain conditions, which can also cause a high idle. BTDT on 2 different cars so far.

Absolutely start with the easy stuff first though, TB and TPS stage 0 are must have's. The missing VSS seems to cause a much higher idle more often from what I've run across, but not all cases seem to be identical.

gsellstr said:

Something not commonly mentioned is regardless of idle motor, LH can still play with idle speed. The EZK will adjust timing at idle based on certain conditions, which can also cause a high idle. BTDT on 2 different cars so far.

Absolutely start with the easy stuff first though, TB and TPS stage 0 are must have's. The missing VSS seems to cause a much higher idle more often from what I've run across, but not all cases seem to be identical.

Click to expand...

One thing I noticed while testing idle valves is wide open (@62% duty cycle) they can pass enough air to race an unloaded engine much in excess of 3K* rpm provided the TPS idle contacts are not closed. When they are closed, the fuel will be repeatedly cut until the RPM falls below some reasonable (yet not 780) RPM.

But yes, ignition timing can do it as well, but I'm thinking the feedback which sets the idle valve opening is done in the fuel ECU using its RPM input from EZK regardless of timing adjustments. Swapping the EZK should eliminate any question.

*Estimated by ear by revving to make the same sound from the driver's seat.

cleanflametrap said:

If you can trust your idle valve doesn't have any sticky places, monitoring the duty cycle inside the car can offer a clue to whether the anomalous extra air is being added by the ECU or otherwise, such as past the throttle. One of my old multimeters has duty cycle/frequency function. It would provide an instant proof at a glance if left on the passenger seat during a test drive.

Testing with a 951 I found the control range to be 25% to 62%.

Click to expand...

Science.

Hmmmm, so I took out the instrument panel to begin checking the VSS wire to the ECU and then proceeded to get to the ECU harness when I saw this underneath my floormat...



Took off the harness...





Flipping moisture inside the connector coming from somewhere. Pretty aggravating since I just had the ECU out not long ago to test some other brain boxes for eBay sales.

At any rate, the carpet is wet, but not sour, so it hasn't been there long. It hasn't been raining much, but I have been running the defroster the past few days which means it could be A/C water. So cleaned the A/C drain with a wire and compressed air, took out the blower motor resistor pack and vacumed out a small stash of leaves, cleaned the ECU pins, cleaned the harness (BTW solid signal between the instrument panel and the harnes), ripped up the carpet and soaked up as much as I could with some towels and propped it up to continue drying.

Drove home and it seems fine for the moment, but I'll have to see how it keeps up over the next few days. It's been an intermittent problem, so it could still be there.

Now where could that water be coming from? Cause I can't really believe it's from the A/C, that'd be too easy. But if it doesn't come back, then I guess the drain was clogged after all.

As always, thanks for the suggestions!! I'll keep ya'll posted.

EDIT: Can't be A/C water... I'm taking off the cowl tomorrow and will get a better look at the air inlet.

Sometimes I lose track of what kind of a Volvo we're troubleshooting. If yours were a 240 I would have displayed this image: http://cleanflametrap.com/wiper2604.jpg

Oh snap, that's a water invasion!

Well when the cowl comes off tomorrow, I'm gonna seal ALL the things.

Look forward to more updates with pics.

A plastic shield comes loose on 700/900s. Take off the windshield cowl and butyl tape the thing back on. Maybe add some silicone.

FIXED!

Had a couple of days to make sure the rain wasn't still finding a way inside and I still have a dry carpet. Wonderful!

Removed the cowl, removed the windshield wipers and the shield to be able to check out everything real well.



The air intake shield was still well glued, but I did find a crack in the cardboard layer that turned into a hole.



Filled it wil silicone, treated the space with a layer of sealant and voil?, no more leaks. Other than that I wasn't able to find anything else suspicious, so guess that's solved.

BTW the car runs fantastic! So the corrosion on the pins was indeed the culprit.

Nice. Another leak point is by the driver's left foot. A plastic panel comes unglued.