Rough idle and misses sometimes when taking off from stops.

Hey everyone. I have a 92 Metro, and it runs really rough. Idles right when warmed up, around 800rpm for a 5-speed manual. However, car shakes way too much (you can easily see the car shaking side to side when it's just idling). Also when taking off from a stop, if you don't give it enough gas, it'll miss and have a really hard time taking off from a stop. Any of you have any idea what's causing this? The timing is right on at 5 degrees BTDC with the connector shorted out as per specs. Just did a full tune-up on the car....plugs, cap, rotor, plug wires, air filter, pcv valve, oil filter, oil change, new iac valve, fuel system cleaner....really have no idea what's causing the rough idling. If any of you have any idea what's causing it, I would appreciate any help you could give me.

Thank you! Looking forward to getting some responses on this issue.

Dan

Sounds like it could be a burnt valve. You can test to see if you have a bad cylinder or burnt valve pretty easily. Just pull off a spark plug wire one at a time, crank the motor, and then see how it runs. If it dies when you pull the wire, you know that cylinder probably is good. If it does not die and runs about the same, you have found the bad cylinder. With everything you have replaced, sounds like a head or cylinder problem.

You might want to see if your MAP sensor is working. Mine failed and caused idle and performance issues that defied my shadetree skills. Finally gave up and let a local shop take a look at it. MAP sensor was dead.

While it was running I did pull off the hose going to the MAP sensor, and the car almost died. So it's partially working at least. I pulled off a hose going to the vapor canister and the car ran a lot better, but idled too high. I ordered a new vapor canister a week ago, going to install it when I get it and see how it runs then. If it's a burnt valve or cylinder, would it be best to get a rebuilt head on eBay for $200? Just curious. Well, let me know what you all think.

Dan

If it is the head, then take it to a machine shop. It will be cheaper and you will also have a guarantee and know it has new parts in it.

Do a compression check on each cylinder. I think they have to be around 175 psi +/-, but don't quote me. A bad cylinder will drop to below 100 psi - which can be an indication of a bad valve. You can get a reconditioned head at partsamerica.com

Just a little update and a little more description of my problem.

The car runs well. Never overheats. I replaced all the vacuum hoses, and blew air through the fuel return hose to the tank. It's clear of blockage, but I think it was slightly blocked before I did that. Now it runs slightly better when idling. Has plenty of power though it seems. Doesn't sound like a burnt valve or bad cylinder though, although I haven't run a compression test yet.

Doesn't blow any smoke or anything out the tailpipe, it's always mostly clear, and normal. I do know the engine uses oil...about a half-quart in 250-300 miles or so. I'm still working on it. I'm getting a brand new carbon canister today in the mail...curious as to how it'll run after I replace it. The engine has over 158,000 miles on it, so it could use a new carbon canister.

Anyway, any insight would be appreciated. Thanks!

Dan

I posted about the MAP sensor earlier. Pulling off the hose to check for its function might not be the best way to test the MAP sensor. My engine nearly stalled too when the hose was removed. Unfortunately, these sensors can fail in a really neat way. They can malfunction and send false readings to the computer which will then send false signals to the TBI-unit.

I'm not saying this is the case with your car, but your symptoms sound identical to mine.

Well I got a map sensor (used one) on Ebay for about $23. When I get it and put it in I'll see if it makes a difference. I checked all the other sensors and whatnot and everything is working fine. Just unsure about the map sensor. I did put in a new oxygen sensor today though.

Dan

I got a MAP sensor the other day in the mail, a used one. Hooked it up, and the car runs much much better. Guess my map sensor was going bad. I'm getting another one in the mail in a day or two (got 2 for $20 each which isn't too bad considering they're like $280 each new). I'll compare the two and use the best one and save the other one for a backup. And I'm sure I'll get some more map sensors next time I go to the junk yard. :) But yeah, my idling is better with a different map sensor. Also the engine so far doesn't try to miss or anything.

I'm glad you replied. A lot of times people make suggeetions and the person who asked the question never comes back to tell how it all worked (or didn't work) out.

Well the car mostly runs better. Still runs rough though at idle. I messed around with the throttle position sensor and moved it....shouldn't have, because I can't remember where it was at the factory settings.

I'm out of trying stuff for now though. Next thing I need to do is take it in and have someone diagnose what the problem is.

I did notice though that when the cooling fan comes on, the engine does eventually increase in idle, but it's erratic. Could all the problems I've been having come from a faulty ECM? Is that possible?

Also where is the ECM located on a 92 Geo? Is it behind the glove box?

Well, any help would be appreciated again. I'll have my 92 Geo Metro service manual next week. But until then, looking for any opinions any of you might have.

Dan

The ECM for your car is above the fuse panel close to the firewall.
You should check also for vacuum leaks and did you cleaned you egr valve passages?

I replaced all my vacuum hoses with new ones. I inspected the EGR valve, it does have built up carbon inside it...guess it won't hurt to clean it out. What's the easiest way to clean it out that's rather fast? Could I immerse the whole EGR valve in something to break the carbon up?

Dan