So I've finally decided to start working on my 99 so that I can get it out of the garage. I figure the easiest way to do that is to fix it and sell it.

So anyway, when I got the thing, it wouldn't start and run. It would start and then immediately die. Turns out the computers got wet from the sun roofs or windshield and the BCU and ECM wasn't talking to each other. So I got a matched ECM and BCU out of a salvage yard, and it starts and runs.

Next problem was a dead miss. I check wires and plugs, everything looked fine. I swapped coils side to side and the problem followed. So I bought a pair of coils.

So now the problem I'm having is that the thing will not idle. It seems to run ok if I press on the gas, but once it goes to idle it eventually drops down to 300-400 rpm and then finally will die. It's not recording any misfires now either. I've tried cleaning the IACV, and I've swapped the known good one off of my 2003 and it still won't idle. I've tried checking for vacuum leaks by drowning the intake in carb cleaner with no results. I seem to have activity from the MAF, TPS, and o2 sensors when viewed with an odb2 scanner.

One weird thing that the 1999 does that the 2003 doesn't do is that just sitting there at idle, the scanner says that I'm traveling at 142.5 km/h. (which oddly enough is 88 mph... perhaps this thing thinks it's a DeLorean). Giving it gas seems to make the numbers change a bit... but the 03 shows an acurate speed of 0 km/h. I'm wondering if this is just something different between the ECM/BCU of the 1999 and 2003...

Does anyone have any ideas of what to check? Anything come to mind that would keep the thing from idling?

 

Doesn't the VSS input come from an average of the ABS wheel sensors? So SLABS is suspect? What about vac leak around the PCV system? Can you attach an old school vacuum gauge and watch it while you pinch off lines?

 

So I disconnected the slabs computer and the odd speed readings were still there. I'll see if I can find a vacuum gauge. I know I used to have one somewhere. Thanks!

 

I would venture to say that your idle stepper motor or IAC is not getting driven

If you removed the intake manifold or more, you may have smashed or grounded a wire.

Or, the driver electronics for that motor are simply blown.
Or the power supply to the driver electronics - a fuse or such
is not working.

You need to trace from a wiring diagram from the IAC idle motor back to the power source for that motor.

As it is bi-directional there will be three or four wires to trace.

With that said, consider this conclusion...
This is a stepper motor.

The windings which drive it OPEN are not intact or the power wires to drive it OPEN are not intact.

It seems to get instructions to CLOSE and keeps closing and closing and then is closed shut. That is why there is no idle.

Trace the wiring with an OHM Meter.

 

EDIT: one thing I forgot: So I found a vacuum leak at the where the plastic booster line hooks up. I plugged the port. No change.

It's makes noise with the key on, engine off, just like the one on my 2003 and it doesn't throw any IACV codes, so I'm inclined to think that it's at least somewhat working. What's funny, is that when I start the engine, it idles at 1200, like the book says it should. Then it idles down to 800-ish, also like the book says. Then it eventually just drops off and start idling at 300-400, sometimes even stalling.

I've tried swapping the TPS from my 03, even though it seemed to have good numbers on the scanner. No change. I unhooked the front o2's. No change. I swapped the MAF with my 03, you got it.. no change.

These Bosch setups are usually pretty good about telling on themselves... which is why I'm scratching my head so hard on this one. So far no new codes.

 

Im assuming when you changed the coils, you pulled the intake? You may have a pinched harness. Trace you problem to when you didnt have the stalling issue, which is when you did the coils.......
..
..
Unless you have baby hands that can fit back there?

 

I pulled the intake. But I cannot go back to before it stalled... when I got the car it was not running. Then it had a bad miss. Now it stalls. It's getting better, but it's still never been "right"

I was pretty careful about not pinching anything. But you're right, I'll probably end up pulling the intake again... just looking for other things to check before that.

 

OK, here is my test and theory for you..

Take the IAC motor from your RUNNING discovery.

Put it into the bad discovery.
BUT DO NOT connect it to the wiring harness.
Just put it in there with no wires.

I bet you will get an idle then.

My bet is that the wires which OPEN your IAC are bad.
The wires which close the IAC are good.

If you have an IAC in the good rover and it is open enough to idle
and you put that IAC in the bad rover - with out connecting it then the setting is frozen - but the IAC is open enough to allow an idle.

Interesting idea to you?

 

I like the way you think Jfall.

 

So I finally got some good tires on this project, and I drove the thing to work this morning... and guess what... I got a code P0501, for the vehicle speed signal. I'm going to take my SLABS out of the 03 and put it in the 99 and see what happens.

Because accoring to RAVE: "The VSS is used, by the ECM, to control idle speed and overrun cut off."