93 convertible M20 jumpy idle and no restart

[Just Scott]

Though I would document what I've found and done:

The situation:

1. The car would start right up from cold, no problem
2. Strong smell of gas from the exhaust, this means rich to me
3. Idle would jump up and down from 700-1500 after maybe 30 seconds or so
4. Engine would eventually stall out and maybe restart, maybe not
5. Spark plugs were black and carbon'd up

Tests and changes so far:

1. Read my Bentleys
2. Tested the water temp sensor - ohms test within spec
3. Tested the crank position sensor - ohms test within spec
4. Tested idle air control valve - ohms test within spec and functions properly
5. Changed spark plugs - set gap about 0.030" - NO IDLE IMPROVEMENT
6. Changed out the fuel pressure regulator and vacuum line to intake manifold - I was going to test the pressure, but this was easier than renting the tester, testing and returning it... - NO IDLE IMPROVEMENT
7. Tested the throttle position sensor - no continuity when closed, continuity when opened - adjusted this all the way - IDLES BETTER NOW
8. Got CEL to work and stomp tested - no codes 1444

Results so far:

1. Wife wants to know whats so interesting in that book
2. Idles OK at 800 rpm, still has a little skip every few seconds - this got better after the TPS adjustment
3. Would not restart after I shut it off - on to this problem...

I edited the cranks sensor test because I tested the wrong end of the plug - yes, sometimes I miss the details....

[jlevie]

Tested the crank position sensor - tested 80K ohms vs a spec of 540 ohms

And you haven't replaced it. That is way out of spec and is probably part of the problem.

Tested the throttle position sensor - no continuity when closed, continuity when opened

The adjustment could have been off, but there is no way the idle switch should close when the throttle opens. Replace the TPS and correctly adjust it.

The first action should be to replace those defective parts. Then run the fuel system tests in the Bentley manual and repair if indicated. Follow that by having a shop run a smoke test on the intake.

[Just Scott]

I agree and thanks for the advice. The crank sensor is on the list to do tomorrow. Retested after looking at the replacement parts - helps to test the sensor end of the plug...

The TPS is supposed to show continuity on the close and the open, just depends upon which tabs (2&18 or 18&3) you test.

Both of these are available locally, but not as Bosch. Autozone has both of them in their brand... Maybe the local shop has some Bosch on the shelf. Any thoughts on the AZ house brand?

[jlevie]

There are two switches in the TPS, an idle switch and a WOT switch. If the idle switch isn't working the DME won't know to control the idle with the ICV.

The AZ TPS and CPS should be okay. I'd rather have the OE parts, but those should work.

[Ceeker]

I have an 87 vert; when I got the car I had the same problem. it was flaring up like a pack of hemorrhoids. :-)

I started with the ICV - no change; TPS - no change: checked for vacuum leaks - no change; since cars after 87-93 don't have a separate control unit for the ICV you can't change or adjust it. The ICV control is built into the DME.
changed the thermo switch/temp switch - no change.

My tack was still bouncing - idle was still flaring. I asked my bmw tech friend and he said the only likely thing left. the DME. Told me on occasion he has seen this problem in the past.

I was lucky to have a ton of parts lying around to test. I threw another DME in and the problem was solved.

Just thought I'd share my experience.

[Just Scott]

Got the CEL to work tonight by fiddling with the bulb and connections - stomp test shows 1444 = No codes.

Yet to do - replace vacuum lines and such. I'll probably clean up the TPS a little more and fine tune the adjustment.

Also pulled a nonworking Clifford alarm system out of the car - didn't know it was there, but found it when I was working with the gauges.

[Just Scott]

Replaced the fuel filter today - not a specific reason - just thought it would be a good idea.

I learned first hand how sensitive these cars are to vacuum leaks. Honestly, I thought everyone was exaggerating. On a running car, the dipstick pulled out will cause it to stumble. Pulling the oil cap will make it stall. WOW. My rough idle was cured by putting a hose clamp on the manifold to FPR hose.

The intemittent non-running issue is apparently the DME relay. When the car would die, the CEL wouldn't come on. I jumpered 30 to 87 &87a and she starts and runs like a top. Solid idle at 800 rpm.

Now my speedo doesn't work, not sure if it ever did, but I did just pull the instrument panel, so something probably came loose.

[nando]

check for broken wires at the sensor in the diff