Switching on headlights causes rpms to drop dramatically.

[grocery_getter]

On the flipside, I've had to troubleshoot a '91 that will not idle worth a damn and I traced it to pin 6 and 14 being backward in that car. Flip the 2 pins at the ecu end and idle is good!

 

[stevep]

Flipping the pins takes all of 20 seconds now and I can almost do it in the dark.

 

[cheekychimp]

LOL I wish you lived closer then. It took us ages last time. I'm sure once you have the technique and know how much pressure is required to snap them loose you have the confidence to just do it, but after reading the how to and having visions of breaking the connector and having to re-pin an entire ECU connector we were probably being too gentle.

It's really immaterial at this stage. It could take several hours at this stage and after everything else we have gone through with this car it would still rate as a 'quick fix' /ubbthreads/images/graemlins/rofl.gif

 

[bazeng]

My car also does the exact same thing. Does any pdt know exactly what the ecu is doing when controlling idle?

Input - process - output?

Disregarding the ac switch + ps switch inputs. Only interested in the core operation of idle control.

My situation is a little different. I'm using a mote to control ignition and fuel while the stock ecu controls only idle. The only inputs and outputs I have wired to the stock ecu are all related to idle.

Inputs connected:
Rpm
12v constant
12v ignition sw
Ac
Ps
Afm sin wave generator ay approx 30hz
Idle switch
Tps

Not connected but might be relevant but not sure:
o2 narrow sig
Water temp sig

I'm running hks 272 cams idling at 1200 rpm. does the ecu also need to be mapped to idle at 1200rpm?

 

[cheekychimp]

Quoting fuel:
when you put the steering on full lock does the ECU attempt to bump up the idle speed or do revs drop also?



Mate, what were you thinking about here? I originally thought you were simply trying to establish if any extra draw on power made the rpms drop. Since I established rpms do drop on full lock however and since my problems occur mainly at low speed, I am now wondering if the power steering sensor is buggered as well. I don't think it's the only issue but it could be exacerbating things. I haven't located an EVO TPS to wire in yet, but as an experiment we unplugged the throttle closed switch on Ken's car and couldn't get his car to do what mine does, so whilst I don't discount what has been said, I also think there is a problem causing my idle to drop significantly so that it requires the ISC to intervene. It certainly seems that in general if things are set up well, the idle remains steady enough that the ISC just isn't needed.

 

[cheekychimp]

I just wanted to update this thread to say thanks and that a combination of issues were addressed over the last few days, which have not only resolved my problems but dramatically improved the whole feel of the car. I cannot say exactly which issue was the main culprit. Most likely it was a combination of several of them.

We still are not sure why the idle switch being disconnected on Ken's car causes no issues for him but clearly leaving it like that is pointless if you retain an ISC so thanks Andre, we have addressed this with a four wire TPS. we swapped in another ISC which smoothed things out but didn't stop RPMs dropping under load. So we then swapped in another alternator and an HKS grounding kit that I picked up from Cory together with some heavy gauge wire to run from the alternator to the battery. This stopped the rpms dropping by more than a minimal amount. A new battery might be a good idea!

As mentioned in the last post, the power steering sensor was also clearly not working. Again I don't think it was the cause of all the issues but it undoubtedly contributed significantly to the stalling issues I experienced during parking or maneuvering at slow speeds.

Another radiator was also fitted but that was a separate issue with the radiator cap not sealing and spewing coolant the whole time. I was just getting tired of adding coolant and cleaning up the mess.

So, I'm very pleased at present. I'll see how things go over the next few weeks and if any issues come back but I think in general the electrical system just wasn't up to scratch and as usual a few 20 year old parts had just given up the ghost.

Paul.

Edit: Just wanted to update this and state that the idle has remained rock solid since I last made this post with no new idle issues whatsoever. So in my case these issues were corrected by the replacement of the power steering sensor (to bump up the rpms) and the fitment of the following: -

(1) an older brown coloured JDM ISC (part no. unknown);
(2) an EVO III 4-wire TPS (since the S90 throttle body had no TPS switch);
(3) a working higher amp alternator (plus a thicker gauge charging wire from the alternator to the battery); and
(4) an HKS grounding kit