1990 Chrysler Le Baron Rough Idle

SCCOSYSTEMS

MEMBER
1990 CHRYSLER LE BARON
110,000 MILES

I have a 1990 Chrysler Convertible with a 3.0 litre engine and automatic transmission. When I first start the car, it has a smooth quiet idle and plenty of power. Once it reaches the normal operating temperature, once I stop it then try to restart it, the idle is erratic. The tach will just up and down from 750 to 1500 rpms, then cut out. If I try to restart it immediately, it won't as if it's not getting either fuel or spark. If I let it sit for about 5 minutes, it will start back up and run smooth once again, with no movement of the tach needle. It idles then at 1100 RPM in park and 750 rpm while idling in drive. I have checked the codes after reseting the computer. They are 12 (no biggie) 35, 42, 54 and 55 (end of codes). I changed three of the 4 relays under the hood. The only one left is the starter relay, which seems to not be a problem. This car does not seem to have an EGR valve or an Ignition control module attached to the distributor. The ASD relay has been changed. Any suggestions?

Monday, June 10th, 2013 AT 4:57 PM

3 Replies

CARADIODOC

MECHANIC
34,082 POSTS

54 - camshaft reference circuit not detected

Based on the multiple symptoms I think I'd head to a salvage yard and fetch a different distributor to try. Those on the 3.0L give extremely little trouble but that's what it sounds like. There's two optical pickup assemblies in it. (My daily driver is an '88 Grand Caravan with the 3.0L and I have an '89 Grand Voyager with one too). One pickup is for low speed and one is for high speed. As I recall, the high speed one means anything above cranking speed.

If the problem occurs when it's raining or during periods of high humidity there could be moisture condensing on one of the optical pickups. The clue is the engine will start after the heat from running it a few minutes earlier migrates up and burns that condensation off.

Your engine also uses a crankshaft position sensor. Those often fail by becoming heat-sensitive. They fail when that engine heat migrates into them, commonly from the lack of air flow right after the hot engine is stopped, then they work again when they cool down, typically after a half hour.

In this case the fault code is for the camshaft position sensor. That's the optical pickup in the distributor. If the signal is missing from either the cam sensor or the crank sensor, the Engine Computer will not turn on the automatic shutdown (ASD) relay during engine cranking. That could result in the code 42 and it WILL result in a no-start condition. That relay sends current to the ignition coil and injectors.

Code 35 refers to the radiator fan circuit. We'll tackle that next if necessary.

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Monday, June 10th, 2013 AT 9:54 PM

SCCOSYSTEMS

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2 POSTS

Thank you. You were 100% correct. At first I thought that it was either a pick up coil or Ignition Control Model.I even ordered one. But I soon found out that, in the convertible, the distributor is solid state and needed to be replaced. Thanks for your response. Luckily, I brought it to a place with an old school mechanic who was able to diagnose it and he took care of it. But, I want other readers to know, that the first two places that I took it to told me that it would cost more than the car is worth to diagnose the problem, they immediately looked to checking all the wiring on the harness, the slow bleed method so to speak. Obviously, you do know your stuff. Thanks again :-)

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Wednesday, June 12th, 2013 AT 6:56 PM

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