Strange, intermittent start-up behavior

[bytes311]

The first time this happened (about a year and a half ago) I chalked it up as some bizarrely rare anomaly, but then it happened again today.

My car sat in the sun/heat for a couple of hours (as it did the first time this happened). When I went to fire it up, it started fine, but I noticed the RPM gauge was stuck at the 1000 RPM mark as if it wasn't registering RPM's. I gave it a little throttle but the RPM needle would not move and the engine sounded like it wanted to die. I turned off the car and immediately started it back up. The gauge came back to life and everything worked normally again.

This is such a bizarre intermittent issue that I really don't know where to start looking. Faulty Lambda ECU? Perhaps you guys can point me in the right direction.

Thanks!

[Bitsyncmaster]

My first guess would be the tach gauge is bad but if your engine was running different than I would say an electrical problem. I guess it's possible a bad gauge could affect the ignition since it uses the ignition to display the RPM.

[bytes311]

My first guess would be the tach gauge is bad but if your engine was running different than I would say an electrical problem. I guess it's possible a bad gauge could affect the ignition since it uses the ignition to display the RPM.

Maybe something funky going on with the ignition ECU?

[MrChocky]

The first time this happened (about a year and a half ago) I chalked it up as some bizarrely rare anomaly, but then it happened again today.

My car sat in the sun/heat for a couple of hours (as it did the first time this happened). When I went to fire it up, it started fine, but I noticed the RPM gauge was stuck at the 1000 RPM mark as if it wasn't registering RPM's. I gave it a little throttle but the RPM needle would not move and the engine sounded like it wanted to die. I turned off the car and immediately started it back up. The gauge came back to life and everything worked normally again.

This is such a bizarre intermittent issue that I really don't know where to start looking. Faulty Lambda ECU? Perhaps you guys can point me in the right direction.

Thanks!

This doesn't sound entirely different to what I'm seeing, but in fairness, I haven't seen it enough to properly categorize it. In short, it's an apparent cold start issue; the engine will start, but
will then die, or not take any more throttle or run rough. This is approximately correlated with starting on a hot day (although the car's in the shade) and starting with the A/C running,
but those again are poor observations. I've yet to do any of the usual diagnostics for cold start.

I will note that the car had some microswitch adjustment last year for stalling with the A/C running at stops, but I don't how related the idle system is.

[David T]

Look for a bad connection that is temperature sensitive in the engine ignition system.

[bytes311]

This doesn't sound entirely different to what I'm seeing, but in fairness, I haven't seen it enough to properly categorize it. In short, it's an apparent cold start issue; the engine will start, but
will then die, or not take any more throttle or run rough. This is approximately correlated with starting on a hot day (although the car's in the shade) and starting with the A/C running,
but those again are poor observations. I've yet to do any of the usual diagnostics for cold start.

I will note that the car had some microswitch adjustment last year for stalling with the A/C running at stops, but I don't how related the idle system is.

Sounds like I'm not alone! In my case, the engine starts and idles fine until I give it gas... then it sounds like it's starving for fuel like something's disconnected. Whatever signals the RPM gauge I suspect.

Look for a bad connection that is temperature sensitive in the engine ignition system.

Anywhere to look in particular, inside or outside of the car?

[David T]

Anywhere to look in particular, inside or outside of the car?[/QUOTE]


Unfortunately there is no simple answer to give you. A bad connection could be anywhere including the grounding. I would start by going over the wiring to the tachometer.

[MrChocky]

Sounds like I'm not alone! In my case, the engine starts and idles fine until I give it gas... then it sounds like it's starving for fuel like something's disconnected. Whatever signals the RPM gauge I suspect.


Anywhere to look in particular, inside or outside of the car?

At the risk of jinxing things or saying something irrelevant, since I replaced my plugs, wires, distributor cap and rotor, I've not had any cold start problems.

However, I definitely still have idle problems and stalling at idle when running AC, so vacuum lines are next.

Sent from my Pixel 3 using Tapatalk

[David T]

When looking for vacuum leaks you must also check the injector seals, the air pipe for the idle motor, missing or stripped out bolts, etc. Point is, vacuum is sneaky and can leak in a lot of places. The best way to find them is to use a smoke machine. A lot of tiny leaks are cumulative, they add up to one big leak so you should try to fix them all. The better you can do it the more effect the idle motor can have and the better the idle. When running the A/C you add a LOT of load on the motor. Not just he compressor, the alternator is also working harder because of the fan motors so the idle motor is supposed to be able to increase the airflow to hold the idle up.