2.4LH swap idle problem

[Group A]

We did a B230FT and LH 2.4 swap on a 80 262 Bertone (k-jet V6).
Engine harness is from an 89 240.
Motor and ECU's are from a stock 92 940T.
M46 trans with stock lh2.4 dogdish flywheel.
Head was rebuilt, shaved and ported lightly.
RSI Stage 1 cam.
RSI adjustable cam gear.

Car runs and drives beautifully except for the below idle problem.

Problem we are having is it will idle at 1300-1500rpm after driving it and revving it to approx 6000rpm.

Idle is set to 900rpm. Idles fine during cold, warm, hot and after free revving up to 6000rpm. Always drops back to 900rpm. UNTIL you drive it and rev it to approx 6000rpm (I'd guess 5500-6000rpm), then it idles at 1300-1500rpm. You can drive it civilly and it will still idle at 900rpm.

I let it run for 10-15 minutes hoping it would drop down to normal on it's own. Doesn't.
You can however turn the ignition off, restart it immediately and it idles at 900rpm again.

Swapped out ECU's and IAC's with known good working ones. Nothing changed.

Throttle body has been cleaned.

TPS is set (switch clicks just as it should).

Coolant temp sensor is working (could be wrong year model?).

Diagnostic code shows a 311 - "Vehicle speed signal missing" (we are not using an electronic speedo)


I've checked and looked over everything I can think of at least 5 times and I'm out of ideas.

Any ideas?

 

[740Weapon]

I have said this before in other threads and i will say it again in this thread.

LH2.4 absolutely will not idle right without that speedometer signal.

IMO you have two options. put in a tone ring setup and wire it up correctly or ditch the IAC completely and run only the throttle stop for idle control.

 

[Captain Bondo]

What is the ignition advance at "normal" idle" and what it is at "high" idle? What is the vaccuum at both?

I can't see speedo signal affecting idle speed.

 

[andysbeta]

With the VSS signal missing to the LH2.4 ECU the idle will indeed do that as you describe. The ECU references vehicle speed as part of its operation , and uses it for referencing the idle control too.

I went through that last summer with the 80 244 I did, and was only able to correct it by finishing the conversion to tone ring rear end, and electronic speedo. I have had thoughts of perhaps using a 240 ABS spindle/pickup just for that reason, as all I from what I gather is the ECU really needs to know is the car is stopped so it can do idle control correctly.

 

[Captain Bondo]

Interesting - some management systems do actually open the IAC on decel as it smooths out the "trailer hitching" sensation you get if you go on/of the gas in a manual trans car.

Perhaps it thinks it's in decel. You'd think since it never registered the car was moving, it would never think it was decelerating, but stranger things have happened.

EDIT- Sounds like it does this just revving in neutral though, right pat? In which case it really shouldn't know if it has a speedo signal.

Maybe it's picking up noise as the engine revs. I would jump the speedo input to GROUND. It should always read zero speed and acxt like a "normal" car. You won't get the cool IAC decel feature but who really cares?

Seriously, try grounding that pin.

 

[Group A]

EDIT- Sounds like it does this just revving in neutral though, right pat? In which case it really shouldn't know if it has a speedo signal.

I can rev it to the moon while parked and it always returns to normal idle. It only idles high after revving it way up on a drive.

 

[Hodginsa]

Its the speed signal, no one will believe this for some reason... But really, try what captain said! This would be really interesting progress since anyone with LH could do this and their cars would suddenly start fully cutting fuel on overrun, and actually slow the cars down more.

Another test though, get the car to do that, then unplug the AIC and see if the idle drops.

I'm not sure grounding it would do the job since its a VR signal is it not? but anyways give it a try, and if that doesn't work another silly thing you could do is hook up the speed sensor to the ECU but just tape it up somewhere in the wiring, so it never thinks the car is moving.

 

[Captain Bondo]

I'm not sure grounding it would do the job since its a VR signal is it not? but anyways give it a try, and if that doesn't work another silly thing you could do is hook up the speed sensor to the ECU but just tape it up somewhere in the wiring, so it never thinks the car is moving.

VR signals watch for "zero crossing" and can therefore be susceptible to noise. Grounding it would keep the voltage at zero and it would therefore never cross zero and never trigger. Re-reading the problem though, I don't think that will fix it.

Given that it only does it when driving and not when in neutral, it seems like maybe it knows when the AMM sees a certain amount of load that the car should indeed be moving, but it isn't seeing that it is - in which case you're kinda screwed.

In other words, it expects to see the car moving (VSS Pulse) once the AMM load exceeds a certain level.

Easiest way to test that would be to put a vr on a small bracket temporarily wired under the car, reading a hose clamp on the driveshaft.

 

[Group A]

This is most definitely it.

It did seem to drop rpm a little slowly when letting off the gas. It also pops through the exhaust on decel more when it's in the high idling mode. It's all making sense now.

Thanks everyone (yes, even you Andy ).

I'll try out the suggestions tomorrow and report back.

 

[y-bot]

This is most definitely it.

It did seem to drop rpm a little slowly when letting off the gas. It also pops through the exhaust on decel more when it's in the high idling mode. It's all making sense now.

Thanks everyone (yes, even you Andy ).

I'll try out the suggestions tomorrow and report back.

I forgot to mention this morning that I did hear the exhaust pop once as well. Sorry to hear that the idle thing is turning in to a pain.

 

[Group A]

I forgot to mention this morning that I did hear the exhaust pop once as well. Sorry to hear that the idle thing is turning in to a pain.

3" exhaust tends to gurgle on decel a bit normally. It didn't register that it did it more often and a bit louder until someone said something about it. Then ding! The light came on in my head.

We'll get it figured out and hopefully we'll all move one small step forward as a community.

 

[thelostartof]

Does it have a bov?

 

[Group A]

Does it have a bov?

Stock BPV in the 13c.

 

[thelostartof]

Ok then scratch my thought

 

[Captain Bondo]

Speed sensor makes perfect sense given that it does it only after a drive an never at a standstill.

I was skeptical at first but it makes sense now (unfortunately).

The real question now is how does one trick it?

 

[Krisverde]

My car does this also, I wired up the speedo signal, still get 311 code.

 

[sbabbs]

So you've figured it out? What is it then? I drove my 89 around for months when I first got it running without the speed sensor hooked up and had no problems with idle driving around in town and all that. Recently I put that Yoshifab 960 throttle body adapter on and I am having some problems with it not idleing down when I take my foot off the throttle all the way while cruzing. I can tell its the throttle body not closing all the way because my wideband does not go to 34 instantly when the ecu cuts fuel when I take my foot off the gas and the TPS tells the ECU it's closed. It seems to me that the spring isn't strong enough to keep the throttle plate closed all the way at decel from the vacume of the motor. I can tap the throttle and it then comes down. I might just need to adjust the TPS sensor. I don't really care to much as this is not that big a deal as I don't drive the car all the time and since I tightened up the nut holding the throttle spool, it doesn't seem to do it as much. I'll unhook the speed sensor again and test this other theory about how LH2.4 won't idle correctly without it. Maybe I should check my codes anyway.

Simon

 

[terrortore]

Problem we are having is it will idle at 1300-1500rpm after driving it and revving it to approx 6000rpm.

Idle is set to 900rpm. Idles fine during cold, warm, hot and after free revving up to 6000rpm. Always drops back to 900rpm. UNTIL you drive it and rev it to approx 6000rpm (I'd guess 5500-6000rpm), then it idles at 1300-1500rpm. You can drive it civilly and it will still idle at 900rpm.

I let it run for 10-15 minutes hoping it would drop down to normal on it's own. Doesn't.
You can however turn the ignition off, restart it immediately and it idles at 900rpm again.

Diagnostic code shows a 311 - "Vehicle speed signal missing" (we are not using an electronic speedo)

I have this "condition too, i get the 3-1-1 code

its popping a lot less on decel now after installing a 3" 012 amm
the idle is still out of control,

before i installed the 100ah 940 alternator it would go too low when the e-fan engaged sometimes stalling.

the car 1993 240
engine 1995 944 b230FK
harness: 1993 240
fuel ecu 984
ign ezk 219
stock vdo odometer (electronic)

 

[JW240]

to get the speed signal it would be worth it to look where the old cruise control gets its signal. Even on my brothers 1982 760 there is a pin on the back of the cluster for the LH/cruise speed signal. Works perfect, just plugged it in.

I have this "condition too, i get the 3-1-1 code

its popping a lot less on decel now after installing a 3" 012 amm
the idle is still out of control,

before i installed the 100ah 940 alternator it would go too low when the e-fan engaged sometimes stalling.

the car 1993 240
engine 1995 944 b230FK
harness: 1993 240
fuel ecu 984
ign ezk 219
stock vdo odometer (electronic)

speed-signal hooked up correctly?

 

[terrortore]

probably not,. not sure how its wired, do the odometer get the signal first?

the odometer/speedo works fine though.

where should i hoooook it up behind the cluster??