Nearly Stranded Tonight

[Shock(/\)ave]

I was driving my girl's 1988 320i with her in the car tonight, when we were nearly stranded in a parking lot.

For the last few times I've driven the car, very shortly after beginning my journey the car would momentarily lose power and pick right up again, never repeating the behaviour for the remainder of the trip or after being restarted when parked for short periods of time.

Two days ago I charged the battery with the hood open, and some very light snow blew into the engine bay. (I'm not sure if this is relevant, but snow could potentially have fouled some sensor somewhere.)

We took the car out to run errands tonight - without any heat as the heater core started to leak on me and I haven't placed an order for the required parts yet - and the car started fine and idled well as it warmed up.

After stopping for our first errand and starting the car again, the idle surged and dipped uncontrollably regardless of where I moved the throttle with my foot. The dips in the R.P.M. were serious enough that the car would almost stall, with the battery light appearing then extinguishing. This carried on for several minutes until I was finally able to get the car moving in first gear - jerking along with the surges and falls in the throttle - and eventually into second gear.

With these cars having a cable operated throttle I was very surprised to find myself in a situation where my throttle inputs had literally no perceivable effect. No codes were thrown whatsoever!

I was able to limp the car home, though pushing the pedal too far toward wide open would cause a loss in power and would require feathering to regain any throttle whatsoever.

When the car was on throttle, the motor was strong and ran perfectly.

Does anyone have any idea what the heck is the issue with this car?

[berlow94]

Vacuum leak...
Check Ya hoses son!


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[cabriodster87]

Might be a whacky temp sensor. (the one to the ecu)

[heatmakerz]

Vac leak. I would also check the AFM.

[Shock(/\)ave]

A vacuum leak can cause crazy random havoc like this and pretty much make the gas pedal as useful as the mirror adjustment switch for controlling the R.P.M. of the motor?!

I've never heard of that before, but I'll certainly check for some sort of tear.

Thanks for the replies so far!

[Shock(/\)ave]

I just started the car after letting it sit since the night it went haywire. It stalled once, then started and idled fine.

I took it for a test drive after it warmed up, and it drove perfectly and revved without bogging. :)

I parked it, then attempted a warm restart and it restarted without issue again. :D

It's very cold and very windy outside, but I attempted a propane enrichment test to find a vacuum leak and came up without any leaks.

Is it possible that a weakened battery combined with moisture could cause the E.C.U. to freak out and the car to rev randomly (this was not simply up and down between two points, but stumbling all over the place as if I was constantly pushing the gas pedal varying amounts), then prevent it from reaching higher revs (losing power until I backed off enough) once under way, all without throwing a check engine light?

I really need help figuring this one out, as if I were any further away I'm not sure it would have been safe to drive home.

I'm happy it's working fine now, but I'd like to figure out (or at least narrow down) the issue(s) so I can make this car reliable enough to count on for daily duties.

Thanks in advance!

[Shock(/\)ave]

One more thought: could blowing snow that settled into the engine bay, then melted after our first trip into the C191 harness connector, have caused these issues?

[McGyver]

it's hard to diagnose it without seeing the car, but having the dash go wonky, are you sure your battery/alternator are working correctly?

when it bogged down under WOT, that reminds me of my fuel pump going out. it could maintain pressure all day at idle, but dropped to 10-12 psi under WOT. although, i highly doubt you have a bad pump causing this.

[Exodus_2pt0]

Check your coil. Also look for any loose grounds. My first suspicion is a bad coil.

Snow under your hood has about a 3% chance of damaging anything. Unless your coil is cracked and moisture got inside, grounding it out. I've seen this happen, and once the moisture dries out the problems go away until it gets humid again.