Guess my car problem
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Citrislazer
Posts: 312 Member
Okay MFP Garage Peeps, let's test your troubleshooting skills. :-D
Just this week, my winter beater/commuter car (94 pontiac grand am 3.1L V6 195,xxx miles) started to idle rough when cold. It starts strong, idles fine in park, and idles fine once up to temp. No code lights on the dash. However, when I back out of the driveway after starting it, drive down the street a bit, stop at the stop sign for 5 or more seconds, it'll start to stumble and progressively worsen until it's idling really rough (shaking the car kind of rough). Throwing it into neutral doesn't seem to stop it either. There's a little hesitation when I accelerate after rough idling, but that seems to pick back up and the engine/car feels fine while driving. I think I also hear some minor surging of the engine when breaking.
A few other things that may come into play. My car is driven 5 miles to work through lots of stop lights, and 5 miles back the same route each work day. Not much more. The coolant has an extremely slow leak somewhere, but there are no obvious leaks. The coolant looks normal. The oil looks normal and level is good (virtually no loss). The air filter is replaced yearly. My in-town gas mileage has seemed worse than normal this winter.
I'm hoping my car will get me threw til the end of the week without any huge problems when I'll have a chance to look at it. A few things I plan on doing this weekend include changing spark plugs and wires, and replacing the fuel filter. These were on my list of things to replace this summer any way. Fingers crossed that this is an easy fix. If not, where would you start? Got any other diagnosing questions?
Just this week, my winter beater/commuter car (94 pontiac grand am 3.1L V6 195,xxx miles) started to idle rough when cold. It starts strong, idles fine in park, and idles fine once up to temp. No code lights on the dash. However, when I back out of the driveway after starting it, drive down the street a bit, stop at the stop sign for 5 or more seconds, it'll start to stumble and progressively worsen until it's idling really rough (shaking the car kind of rough). Throwing it into neutral doesn't seem to stop it either. There's a little hesitation when I accelerate after rough idling, but that seems to pick back up and the engine/car feels fine while driving. I think I also hear some minor surging of the engine when breaking.
A few other things that may come into play. My car is driven 5 miles to work through lots of stop lights, and 5 miles back the same route each work day. Not much more. The coolant has an extremely slow leak somewhere, but there are no obvious leaks. The coolant looks normal. The oil looks normal and level is good (virtually no loss). The air filter is replaced yearly. My in-town gas mileage has seemed worse than normal this winter.
I'm hoping my car will get me threw til the end of the week without any huge problems when I'll have a chance to look at it. A few things I plan on doing this weekend include changing spark plugs and wires, and replacing the fuel filter. These were on my list of things to replace this summer any way. Fingers crossed that this is an easy fix. If not, where would you start? Got any other diagnosing questions?
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Replies
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Almost sounds like fuel issues, plus perhaps the short journeys has coked it all up a bit - have you given it a damn good thrashing and see if that helps?0
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So basically when you let off the gas, it gets worse...
I would look at the fuel pressure regulator myself. The FPR should be vacuum controlled so don't rule out a vacuum leak. Especially with those kinds of miles.
When the Fuel Pressure Regulator starts to go, it basically dumps too much fuel into your throttle body and the air mixture cannot keep up. Basically flooding the engine. When you give it gas, you are opening up the throttle body and allowing more air to come in.
At idle however, it just keeps on dumping too much fuel in instead of bypassing it back to the tank.
Also, your coolent leak, the GM 3.1 engine was known for crap intake manifold gaskets.
As a matter of fact, there is a TSB out concerning them. SOmething about using plastic tabs.
Anyway, check for vacuum leaks and home in on the Fuel Pressure regulator.0 -
@ Cat
Last time was the beginning of October. I remember, cuz my boyfriend and I raced our crappy commuter cars one night before it started snowing just for giggles. I got a bad start as I was busy trash talkin' to him out the window, lol. But, I did pull it out in the end by a hair. To be fair, his commuter is a mid size, 4 banger car. Wasn't really a fair race.
Can't really thrash the car right now as it's snowing and still icy out. :-( But, I could park it and rev the engine high for a while. I do that every so often with the Camaro if I haven't ridden it hard for a while. The pontiac does get fuel injector cleaner every so often, but I haven't done that for a while now. I'll fuel up the car tonight after work, add some injector cleaner, and rev the hell out of it. My neighbors are gonna hate me tonight! I'll report my findings after tomorrow's morning commute. :happy:0 -
@Bill
You're right about the crappy gaskets. They were replaced somewhere around 125,xxx.
I'll add the fuel pressure regulator test to my check list.0 -
I'll second the vacuum leak. Had similar problems with rough idle on the girlfriend's car that was a tear on the intake boot. Common enough of a problem on the late model Proteges that they actually had it in stock at the dealership.
Does it have a way to monitor the O2 sensor to check for a rich/lean condition during the rough running period? Since it is a 94, I'm assuming it is OBD1. Both ODB1 cars I have done diagnosis on had a way to monitor this through a light or a pin out on the diagnostic connector, but those were not GM vehicles.0 -
@rally
Nah, I don't have a scanner. It needs more like a OBD "1.5" (odd year 94-95), so the cheaper old scanners are hard to find and the new ones are expensive considering it's a crappy winter car. I've checked codes in the past by shorting the scanner connection and my check engine light will flash the numbers for the code. Auto stores around here only read codes for OBDII cars IF they're having a good day.0 -
I didn't have a scanner either. On both, they used the same method as your car to read codes with the check engine light.
On one car, there was a pin directly tied into the O2 sensor signal available on the diagnostic plug that I could monitor with a voltmeter. On the other, there were two pins that you shorted and a light on the ECU switched on/off to signal lean or rich. On OBD2 vehicles, I use a cheap Scantool USB to OBD2 connector and my laptop to see live data and pull codes.
Looking further into that model, I'm less sure about a vacuum leak. The engine uses a speed density system, not Mass Air Flow (MAF). On an engine that uses a mass air flow meter, a vacuum leak can cause a lean condition at idle/low loads that goes away at higher engine loads. Speed density systems tend to exhibit a high idle without the lean condition at idle since those systems do not directly measure the incoming air. I would not expect stumbling at idle unless it was a leak at the intake manifold gasket or a stuck EGR valve.
edit: I mean a stumble due to a lean condition. Leak at the gasket could cause only one cylinder to go lean while everything looks okay to the O2 sensor.0 -
Okay, so after gassing up my car, adding injector cleaner and revving the engine for a while, I still had an idle problem. I got antsy last night, so my boyfriend and I decided to stay up late to change the plugs and wires in the freezing cold. (He's so wonderful.
) Here's what we found:
-The plug wire for #2 was damaged internally. The innards of the wire actually stayed attached to the spark plug when the wire was pulled off without effort. :noway: The innards detached from the plug by hand fairly easily. The post on the ignition coil for it was corroded too.
-My spark plugs were extremely overdue (already knew) and looked like they had been running a little lean.
-To get at the back plugs better (the engine sits sideways in the car), the ignition coil unit was removed. Under neath the ignition coil unit was this... bracket with a small box attached to it and a couple of hoses running to the small box. (Sorry, we're unsure what part this is, and I can't find a parts diagram that tells me what it is.) Behind that, there was a narrow black hose just chillin', not a attached to anything. This hose runs along the backside of the engine bay, down long the passenger side of the engine bay to the front, where it disappears underneath the coolant reservoir. Can't tell if it continues on somewhere or connects to the reservoir. It's about 5-6ft long that I could see and had all sorts of bends in it along the way. The small box looked like it had a spot were this hose would fit, so those got plugged together. I have a feeling though, that the hose may pop off again.
-After putting the car back together, I took it for a test drive at 11:30 p.m. to the grocery store to buy some diet mt. dew and green olives. (We had adult drinks afterwards while watching Counting Cars. :drinker: ) It ran pretty good last night and this morning to work, so the major problem seems to have been fixed. However, that doesn't mean this car doesn't have a million other problems that need fixing. :laugh: Today, my hands smell like motor and sparkling peach hand soap, yuck.
Anyone have any ideas what the mysterious hose and small box are? MAP sensor?
Also, suggestions on where to start with the lean fuel mixture?0 -
As far as the lean burn. if it seemed to be isolated to one cylinder? I would say intake gasket leak near that port, you could give it the starting fluid test to see if it has a leak. If it is a lean condition across all cylinders or one bank? it could be due to the hose you found disconnected.0
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Yah, it was across all of them.0
