Gentle accelleration isn't

January 18, 2007 8:20 PM

CarFilter: My car briefly loses power, or in one case stalled, as I accellerate gently from a standing start or after having slowed down to take a sharp corner. Any ideas?

Since my last service (yes it's going back), my three-speed automatic (1985 Isuzu Gemini RB from memory) throws me forward as it loses power for a moment when I'm starting off or accellerating from having taken a corner. Earlier this week it actually stalled as I went around a corner. It seems to only happen at speeds of less than 15km an hour (it won't splutter just because I take my foot off the accellerator on the freeway) and it doesn't happen if I jam my foot down, rather than starting off slowly. I'm fairly sure it happens when I have the accellerator in a very specific position, but I can't confirm that.

It doesn't appear to be a gear change, because it will happen, then I get my other two gear changes as normal.

It doesn't appear to be affected by the temperature.

It doesn't go away after I've been running the car for a bit.

Forced to guess, with no car knowledge, but some engineering knowledge, I'd say that there's a loose hinge on a valve somewhere such that the first movement causes the hinge to compress and actually choke the valve, before the hinge actually acts as a hinge and the valve starts to open up. I could of course be completely wrong and it my be a clutch or gearbox problem, or something else entirely.

Does anyone have any idea what's going on? I'd really like this fixed during the service I have on Monday because it's not especially safe or pleasant.

posted by krisjohn to travel & transportation (12 comments total)

Is the '85 fuel-injected? Because if it's not, it could be something lumpy sloshing about in the carby and blocking the main jet, or even a lump of crud in the fuel filter blocking the main fuel line. Harder acceleration would be squirting a burst of fuel via the accelerator pump, and would probably temporarily mask the effect of any blockage.

In any case, the fuel filter is an easy thing to check.
posted by flabdablet at 8:31 PM on January 18, 2007

Had a similar thing happen in my gone-and-mourned 1980 Plymouth Reliant (K-car ... those things were solid machines) when it was about 18 years old: a significant notch in the acceleration curve. Changing the fuel filter fixed it, temporarily. It recurred far sooner than fuel filters are supposed to croak.

As near as I can guess, crud from the aging fuel systems was getting caught in the chamber of the filter. At low speeds, not a problem, but increased fuel flow and vibration suddenly kick it up so it gets stuck in the mesh of the filter. Then you lose power until it comes loose and gets itself into a more sustainable position. Recurrence was because older cars are shedding more gunk into the fuel stream.

So that's a guess. My car was a manual shift, so it wasn't due to some gear change I didn't know about; but, conversely, I never just stomped the pedal because, well ... ya gotta shift. Your valve guess sounds as plausible to this non-motorhead. Suggest 'em both to your mechanic.
posted by eritain at 8:33 PM on January 18, 2007

On failure to preview ... yeah.
posted by eritain at 8:33 PM on January 18, 2007

Several things can cause a stall like that. The cheapest and easiest fix would be the air filter if it's dirty. Other items to consider would be spark plug wires and if it is carbureted, your accelerator pump may be bad.
posted by buggzzee23 at 8:44 PM on January 18, 2007

The same thing happens to my 1998 Escort (the stopping part). The idle control is messed up (someone who didn't know what they were doing messed with it and broke some piece), so I have to shift it into neutral when I'm at a standing stop.

eritain and flabdablet are probably closer to correct than I am, but I figured I'd throw this out there.
posted by Verdandi at 8:45 PM on January 18, 2007

I am with buggzzee.. my first thought was the air-intakes. at a certain speed enough air can get forced into the engine to fire. drop below a certain speed and it stalls.
posted by TheOtherGuy at 9:48 PM on January 18, 2007

Thanks everyone.

They were poking around the carby during the last general service and it is already schedulled to be replaced or reconditioned as part of the upcoming service. Sounds like they dislodged some crud which will need to be tracked down.
posted by krisjohn at 10:30 PM on January 18, 2007

I had similar symptoms on my 2000 Honda Passport - it ended up being a cracked air intake which led to a bad fuel-air mixture.
posted by mbd1mbd1 at 7:37 AM on January 19, 2007

TheOtherGuy and mbd1mbd1 are on the right track. Usually a stall or bucking while accelerating is due to unmetered air entering the engine somewhere after the airflow sensor (which is in outlet from the plastic box that holds the air filter). 99% of the time, this is a cracked rubber intake boot. I've fixed this problem on everything from 30 year-old BMWs to two-month old sports cars. They can often be patched with a square of duct tape and a drop of silicone sealant, but will be much better in the long-term with replacement.
posted by wzcx at 8:10 AM on January 19, 2007

My car was very recently doing almost the same exact thing, the stall at lights/stop signs and slowing down to take curves was the IAC (Internal Airtake Control) valve. I also had a bad right battery cable and I also replaced my plugs, wires, D cap and rotor, got an new fuel filter, air filter, crank case breather piece, and an oil change too for good measure.

Last week my starter went, so I empathize and commiserate with you.
posted by goml at 10:37 AM on January 19, 2007

My Neon used to do that. I ignored it too long, and the fuel pump had to be replaced. Stranded me 300 miles from home.
posted by faster than a speeding bulette at 11:00 AM on January 19, 2007

Problem resolved.

I got the car back from service yesterday. They all but replaced the carby (apparently it was impressive that it was still working at all), adjusted the idle control, cleaned/fixed the choke and replaced a fuel filter.

Thanks for help, everyone.
posted by krisjohn at 3:57 PM on January 23, 2007