Was driving home from work (38 miles). Almost home, let off the gas to slow down for the highway exit. The engine stumbled. Odd, I stepped back on the gas and all is normal. Coast up the off ramp and the car is not idling right. Maybe 600 RPM instead of the usual 1000 and very rough. If I TOUCH the gass at all, it dies.


I restart and it idles crappy. I touch the gas (and the clutch) and it dies. Go through this several times before I decide that my own way through this intersection is to get rolling from a 600 RPM idle without touching the gas. The road is level and slippingthe clutch a bunch, I pull it off and I'm half-idling down the street.


Downhill, the car rolls the engine up to 2000 RPM and I press the clutch. The engine revs to 3000 and stays there.


The shop is just around the corner and I chug in there.


That was a week ago. It is not the spark plugs or ignition wires. It is not any of the engine sensors. It is not the fuel. We are loath to "try" a PCM because if that's not it we can not return the new unit.


Is there any place in Houston (or anywhere) that can bench test my computer before I replace it?


David

 

Too add info, this is a 1998 basic SL (single cam engine) with about 119,000 miles. It behaves as if it has a bad throttle position sensor just above idle (if you really step on it, it revs more-or-less normally)but we've swapped in a new TPS with no improvement. Same for the idle control valve and a variety of others.


We really think it's the computer but we would like to have some shop test the computer before we pay for a non-refundable part.


David

 

There are two items to check, the engine coolant temperature sensor (ECTS) and the EGR valve. The original coolant sensor was plastic and prone to cracking while the replacement is the permanent brass one. The two-wireconnector may have corroded and needs to be replaced also, either from a junk yard intake air sensor connector or the dealer $30 part.Have you tried disconnecting the EGR valve wiring connector? This should allow a normal 800 rpm idle and allow normal every day driving as if it weren't needed except for emissions control purposes. When it acts up it can create hesitation, stalling, and erratic engine running conditions. Leaving the connector off is a simple good/bad test for a faulty/sticking EGR valve that can be cleaned thoroughly to prolong its usefullness before the expensive replacement process Edited by: ducky

 

The mechanic says that he tried "every sensor" and I specifically asked him about the EGR.


On the other hand, he did mention that every morning he thought he had it fixed and about the time he was ready to call me it would act up and stay bad. So that points to the temp sensor. I'll ask him to double-check that one.


He says it's throwing a whole slew of codes, none of which make sense to him and he's done the book troubleshooting for each code.

 

If there's a possibility of a clogged catcon there's one way to check for it; remove the O2 sensor (the exhaust will be loud) for another outlet and see if the engine will drive normally.


I work on automated equipment and have found out throughout the years that when a computer spews out a slew of diagnostics misleading one into finding the cause but being totally confused from too many codes that it is another way for the equipment computer to say it lost its mind; a temporary lock-up requiring a complete reboot or the fact that a lack of environmental air conditioning leads to overheating of antiquated computers that the designers never intended the equipment to run in requiring the same reboot. The standard troubleshooting methods don't work but long term experience with the idiosyncracies of equipment and environmental factors, experience, becomes paramount to understanding faults.


In my limited knowledge I have read of only one person, I almost convinced not to do, that replaced his ECM after exhaustive troubleshooting with his patience and understanding of sensors. In this case it appeared to be O2 sensor related but after replacement and tedious O2 sensor measuring with a voltmeter he tried an e-bayECM and voila! The ECM was the problem. All sensors worked properly while the engine warmed up in 'open loop' until going into 'closed loop' mode where the O2 sensor stopped outputting when it was supposed to. The ECM was the problem, not sending a voltage for the O2 sensor to send back fluctuating signals to monitor the exhaust. I don't know if this is similar to your dilemma but you can see the difficulty. There isn't any testing of ECM's as they are built for reliability. There aren't any posts about ECM failures and the one I know about is on the Saturnfans.com site.


Is there a battery voltage issue? Battery and cables must be clean and free of any corrosion including the ground connection.