1994 Geo Prizm/Corolla funky idle

[Deathrunner]

Ok this is a wierd one.

My car is a 1994 Geo Prizm, essentially the same as a corolla. 1.6liter Manual.

The car is having some trouble while driving. It will have a wierd idel that seems to raise and drop. It's almost like the computer is searching for the right mix.

At stop lights, sometimes it will stall out because it is so low. It is even worse with teh AC on.

It is intermitent, sometimes it runs great, sometimes I have to keep my footin the gass and really drag the clutch to get her moving without stalling.

The fuel pump died recently so that is new. It has a new alternator, battery, and clutch.

I put a multimeter across on the electrical system. With all doors shut and car off, I see a draw of 0.296 amps. That seems a bit excessive. So I imagine there is a short and this could be the cause.

Where is the computer located on this model?

Any Ideas as to what is causing this horrific problem?

Thanks so much, Seth

[originalfake]

sounds like time for a new car

[Deathrunner]

That bad?

Too soon to give up.

Where is the cpu located? In my 4runner it is the passenger Kick panel. Same story here?

[REN69]

The ECU is either there or behind the radio as on my GTS. The problem could be a vacuum leak, either that or fiddle with your idle screw until you can get the right setting to stick. I had the same problem with my 89 GTS after I got a so called "throttle body cleaning" done at Mr Lube, fixed it by fiddling with the idle screw.

Original fake...

[originalfake]

im sorry..it would of just sounded cool to hear u decide to get a new car. normally with a car thats somewhat old and experiencing hard-to-handle issues, its probably best to buy a new car because who knows u might a) the problems will come back again due to wear and agin or b) end up wasting more money to fix the car rather than what its worth..or c) repeat a and it creates hassle for u. just some advice

[Deathrunner]

I hear ya, original fake.

Hindsight is crystal clear, though. I just changed clutch, alt, batt, tires, fuel pump. So I'd like to get some use out of those. Had I known this problem were to pop up 3 months ago.....new car it would be.

I'll check behind the stereo and in the kick panel.

I'm not sure that this car has a idle adjustment screw. There is no AFM. or MAF whichever it is called on these cars. I think everything runs off the tps and computer. I could be wrong.

Liek I said, it will run fine sometimes. But as teh temperature gets hot and I increase the load on the system (A/C) it gets worse.

I had it in an electrical shop a month ago and they mentioned a short by the computer. Maybe there is another, so I will check.


What's teh best way to diagnose a vaccum leak?

[REN69]

Not everyone is rich and can change their cars every year, otherwise I'd be driving an XRS right now.

[Piloter]

There's a couple of idle-up valves...ISVs or possibly called ISCVs...that may have gone bad.

The ECU should be behind the bottom portion of the center console.

Edit: Could also be plugs/wires, or a bad fuel pressure regulator. If you can step on the gas as the engine's about to stall out and the car keeps running, then it's probably either plugs/wires or the idle air control valve. If stepping on the gas doesn't help, regardless of whether the engine is warm or cold, then it's probably the FPR.

[Deathrunner]

Thanks Piloter,

It helsp when I step on the gas, so I guess it's either the plugs/wires or the ISV.

If it is related to the plugs/wires, could it have to do with the distributor or coil? It seems like if it were either of those it would be a rough running motor like a miss or something, but when it's smooth it's smooth. When it's having problems it's more like it's constantly surging up and down versus a rough idle.


How would I identify or check an ISV?

Also, the draw I have on the electrical circuit is now 0.672 amps. I wonder if that is playing a part in the demise.

I located the computer, man it is back there.

[Piloter]

It could be something as simple as a worn distributor cap and rotor, too. Check everything from the plugs back to the distributor, that's the simple fix.

The idle air control valve SHOULD be somewhere on the throttle body, but that's just my logic and may not apply. On the 4AGE, there was a separate cold-start idle-up valve on the TB, but I'm assuming with a more modern engine that they combined the two. Probably the standard Haynes/Chilton manual will have more detail on precisely what it looks like.

The current draw you're talking about, is this measured in line with the battery? Are you blowing any fuses? I don't know what's normal range, but the spare power to keep the radio stations memorized and the ECU quietly ticking away shouldn't be anywhere near an amp of current.

[Donald]

Could the current draw be a clock or radio?

[Deathrunner]

I have always hear that 0.020-0.030amps is acceptable. This draw seems enormous to me. No blown fuses and no drained battery, though.

I have a spare cap and rotor, I will try those. Hopefully it's that simple.

[94_Rolla_Guy]

To find your Mysterious current draw put your meter like before and pull fuses one by one by unpluging the fuse look for a drop in current then move to the next fuse, when you find the system thats drawing, trouble shoot it, it may be as easy as you have a frozen relay or a stuck switch thats feeding something power..


As for your funky idle, i would do a few things i will list them from easiest to hardest

- Run some injector cleaner through the gas tank
- Check your spark plugs for wear
- Check your distributor cap and rotor for erosion of the tips of the rotor and the terminals of the cap
- Check for bad plug wires visually, you could also spray them with water from like a windex bottle and listen for misfires and look for arching
- Check the engine grounds you can do this with a ohm meter between the engine to the neg batt post
- Clean the throttle body its gonna be dirty, my advice is take it off the car, take it apart and clean it with special attention to the IAC (idle air control valve) under a little white plastic box thing with an electrical connection if you do use throttle body cleaner, NOT carburetor cleaner, it eats plastic and rubber

[dandxg]

You may want to do what I did pay toyota to hook up to the 100k machine for diagnostic, about 50 bucks, and then replace it yourself. Without I could have never found out that my VSV was causing the check engine light.

[plzhelp]

can anybody tell me where the computer is located on a 93 geo prizm?? I've asked everywhere I can think of and no one can answer me.