MeFi Mechanics--Older Car Issue
March 4, 2014 12:14 PM   Subscribe

My wife and I have a rather old Lexus with low miles. On each of the last two times we took it out, the car shuddered a couple of times (like driving over a bump) and then lost all engine power, conking out in the middle of the road. There was no sound involved--just that little shudder, and then no power. Each time, we had to push it to the shoulder. Each time, the car would start up again with no problem--but would not stay on. Some more details inside--any ideas what's up?

Car is a 1999 Lexus sedan that's up to date with scheduled maintenance. All necessary fluids seem to be topped off.

Each time that the car has lost power, the engine and TRAC lights have gone on, but after a while (i.e., while waiting for AAA and after being parked on our street for a couple of days), the light would reset. When the car loses power, the electric has remained on--radio still going, heat still on, etc. When the power has gone, however, the power steering seems to go as well.

The car is with the mechanic now. When we drove it over, it actually died in front of the shop and we had to push it onto the lot. When the mechanic came out to take a look, the car turned over, and he was able to drive it to a parking space, but he said it actually died again four times as he drove it 15 feet.

He said the OBD is showing over a dozen error codes relating to the electrics and sensors, which he thinks is bogus, and he instead suspects a grounding issue. He's going to give it some more inspection. He said he didn't see any mechanical issues in his work so far.

I trust my mechanic--I like him, I think he's fair, and I think he does good work. But if you have any ideas that would help him diagnose (and fix!) this, that would be great. I'd like to squeeze some more life out of this car, if possible. I'm sure our next question is going to be about replacing it!
posted by Admiral Haddock to Travel & Transportation (12 answers total)
Well, the engine stopped, so all the lights/(some of the)fault codes and loss of steering is pretty normal. The engine isn't supposed to stop unless you turn off the key that also turns off the monitoring so 'engine stopped' is not something they normally see.

The engine drives the power steering. The 'bump' was the engine stalling, so steering assistance loss is normal.

There's zero chance of diagnosing it from this other than luck. It could be a fuel flow issue (was it always at low rpm?) or an electrical issue (ground issue or sensor issue or otherwise electrically disturbing some feed or information to the ECU). There's just no way of knowing without having the car here - "The engine stops" is the only symptom, all the other stuff is effect, not cause.
posted by Brockles at 12:37 PM on March 4, 2014 [1 favorite]

IANAMechanic, but I have a similar problem with my Honda minivan that is caused by the fuel pump fuse falling out or breaking (it is right near the parking break pedal). Having the fuel pump shut off would cause the engine to stop running and the power steering and brakes to fail shortly thereafter with all the electronics running fine as you describe.
posted by Aizkolari at 12:38 PM on March 4, 2014

It wouldn't explain the car immediately restarting, though. Quite the opposite. Wild speculation - while really all this question can get - is not helping, though.

OP: If the car always stopped at idle/low rpm (ie foot off the throttle) this could be as simple as poor idle control and relatively cheap. But if it happened at speed/under normal driving it could be literally anything.
posted by Brockles at 12:40 PM on March 4, 2014 [1 favorite]

I'll second or third the fuel pump. Such was the case with my old car, with symptoms pretty similar to yours.
posted by papayaninja at 12:41 PM on March 4, 2014

In spite of what Brockles suggests, my car would also start up afterward, at least some of the time.
posted by papayaninja at 12:43 PM on March 4, 2014

Response by poster: Thanks for the great answers so far. My personal guess was maybe fuel pump--but that was before the OBD weirdness.

But Brockles may also be on to something with idle control, because the mechanic did say that it wouldn't idle on its own. I could well have had my foot off the pedal when it died--each time I was doing city driving, so there was a fair amount of coasting in traffic.

What the cause of the idle control issue, I guess, is still a mystery.
posted by Admiral Haddock at 12:51 PM on March 4, 2014

I had an issue like this with an old Honda, and it was the idle air intake control valve that had gone bad.

Also had the fuel pump relay go on that car, but that caused it not to start sometimes rather than to stall while driving.
posted by Kriesa at 1:09 PM on March 4, 2014

In spite of what Brockles suggests, my car would also start up afterward, at least some of the time.

Yes, a failing fuel pump potentially could, but a broken or missing fuse definitely won't. The only guesses we can give are the obvious one which any mechanic worth a greasy overall would be checking. First diagnostics are delivery of fuel, air, electricity and then work from there.

OP: Re: idle speed - the most helpful thing is to come up with as effective a means to replicate the problem for your mechanic. List ALL the common factors for the various times it failed (ambient temp, temp of engine (approx), driving style (throttle/no throttle), after hard braking, after no braking. Any commonality).
posted by Brockles at 1:21 PM on March 4, 2014 [1 favorite]

Seconding Brockles. There could be one or several specific causes of this, but we will NOT be able to diagnose this from here. It certainly could be a grounding issue, or a fuel delivery issue, or a malfunctioning mass air sensor, or even two separate issues that are mutually compounding. The car is with your mechanic, whom you trust. Give him time to troubleshoot this. If he's good, he'll arrive at a root cause within a few hours. Do report back and tell us what he finds, though. Hopefully it's something minor to ultimately resolve, and most of the work is simply in determining the true cause of the trouble.
posted by mosk at 1:28 PM on March 4, 2014

Did '99 Lexi have Mass Airflow Sensors? Your description of the failure sounds a lot like when the MAF went out on my 2001 Maxima during acceleration.
posted by Thorzdad at 3:11 PM on March 4, 2014

Could be bad capacitors on the ecu board. Check on this forum. This matches what you ve described.
posted by zenon at 6:39 PM on March 4, 2014

Response by poster: The mechanic found a number of rusted wires under the car that were shorting. He replaced the wires and the car seems to be running fine.

All the same, we think we'll replace it--see my new question!
posted by Admiral Haddock at 7:11 AM on March 12, 2014

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