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Engine Running Rough!; The engine in my car is running rough, fuel mileage is down..
Topic Started: May 24 2013, 01:03 AM (1,360 Views)
EmporerZombie
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Hey guys. I'm Stu and I'm totally new to forums, so forgive me if I'm doing it wrong. I need your help with my Metro, though.

It's a '90, 2 door, 5 speed, 1.0 3 cylinder hatchback with 132k miles. I've owned it for the past 4.5 years. I've been gradually increasing the mileage by doing things like putting the right sized tires on it. I live in northern AZ. I've been averaging about 50 on longer highway trips. It's very mountainous where I live.

Back in Nov of last year it suddenly started acting up. I first noticed it was making a lot of puffing noises (missing) out of the tail pipe whereas I hadn't heard that before. In fact, sitting in the Walmart parking lot I could hear it from the driver seat with the window down. Then I noticed it was driving like crap. The engine would idle rough and shake a lot. Going down the road at higher speeds it would be a lot louder, run rough, have a lot more engine vibration and would be difficult to shift (as if as soon as I let off the gas the engine would slow down and put pressure on the transmission, which would translate to the stick). The road noise is already bad enough, but I'd have to almost shout to my girlfriend for her to hear me over the engine noise. There was a loss of power, and a drop in fuel mileage, although it wasn't terrible.

My brother-in-law suggested I should check for valve lash. So we get a cover gasket and open it up. It's adjusted right off the cam shaft, so that wasn't it. While we had it apart I put new spark plugs in just in case it hasn't had a tune up in a while.

After putting the plugs in it went back to how it always ran. Quiet, smooth (for a 3 cyl), and drove like a dream. I took my dad out and we drove around town. The difference was like night and day. We adjusted the timing for good measure as I was dropping him off, and it ran even better after that.

I figured that the plugs were the problem. I drove it for four or five months, although at times I thought it sounded like it was louder and vibrating again. On St. Patty's day I took it on a 300 mile round trip to Phoenix and it ran great. I got 53 mpg on that trip.

The next time I started it after that trip it was all happening again. Loud, rough, drove like crap. The engine was adjusting the idle speed up to try to smooth it out. I thought maybe I needed to finish the tune up so I replaced the plug wires, distributor cap, rotor, and ignition coil. It still had the problem.
I decided to read the codes since I looked in my Chilton's manual and found out I don't need a reader. It was flashing code 23. After checking out this forum I realized that I should have let it run it's full course of codes, but I think I watched it repeat 3-4 times and then pulled the jumper fuse, so I don't know if there were any other codes along with it. I cleared the codes at this point to see if it would get the same code again in the future.
I checked out the MAT sensor and found it had the appropriate ohms according to the manual. I checked the voltage from the computer, which was a little less than 5 volts. I put it together and it seemed like it ran ok for the trip home. The next time I got in it was running rough again (you'll find this is a common theme while I've been checking out this problem).

I pulled the distributor cap off and checked everything in there the best I could and it seemed to be doing fine. I didn't have a non-magnetic gapping tool, however.

The next time I checked the car, I re-checked the MAT sensor resistance, which again checked ok. I checked the computer voltage, which was ok. I pulled the cannon plugs from the computer module and ohmed through the wires and the MAT sensor. I got the same resistance as I did when checking the MAT sensor itself. I put it back together and cleared the codes (it was giving me code 23 for the second time). AGAIN it ran like a dream for about a week this time.

When it started acting up I checked the codes, and it gave the 'everything is normal' code. But it was running rough. I drove it into town, had lunch, and pulled the computer fuse located under the hood (which is what I did to clear the codes). It ran great on the way home. In fact, I've done this multiple times at this point and it usually runs well after doing so. Eventually, however, it goes back to running rough.

I'm kind of at a loss at this point. I know what it's like trying to trace down an intermittent problem (I'm an HVAC tech), and this is making me sick to my stomach. I HATE when you don't clearly see the problem. :-/

I should add, that in Dec of last year the fuel pump died, stranding me in the middle of the night on the other side of a mountain from home. I towed it home and replaced the pump. This was during the 4-5 month period where it was running like normal. It was running normal before the pump went out and normal since up until two months ago.

I've gone through all the posts on this forum that had 'code 23' somewhere in them but wasn't able to find anything that matched my problem.

Any help you guys could offer would be greatly appreciated! Sorry for the long post.
Edited by EmporerZombie, May 24 2013, 01:15 AM.
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Woodie
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It's a MAP sensor, not mat, but who cares, that's not the point. First off, you should check and clean your grounds, they're a common problem which can cause all sorts of weird problems. The computer and most of the sensors ground on the back side of the intake manifold, below the throttle body:
Posted Image
At 135K miles, you're getting to the point that you should consider it might be worn out. Do a compression test, all plugs out, engine warm, throttle wide open. New is about 200 psi, worn out is below 150psi, all should be even.


Edited by Woodie, May 24 2013, 08:28 AM.
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cwatkin


Yep! Clean the grounds really well and I bet this problem will vanish. I had very similar issues a while back and did this. Things have been great since. I even ran a new and heavier ground between the firewall and the distributor as well as from the dist right to the negative battery terminal at the same time.

1. Remove the grounds.
2. Buff the ground connector as well as the mating surface on the intake with fine steel wool to get it clean.
3. Follow up with carb cleaner on a paper towel to get all the rest of the dirt off.
4. I went an extra step and ground the paint off the firewall where the ground meets. It was basically grounded to paint.
5. I purchased silicon electrical connection grease like that used for bulb connections, battery terminals, and such and smeared it all over any of the contact points and then re-assembled.

My car had more problems on cool and moist mornings so I was figuring it was something electrical. I would keep it barely running for like 10 minutes and then it would start running like a champ. I figured I had burned a valve when this first happened but then the car would run perfect for the rest of the day. Your symptoms sound almost just like mine.

My car had been so messed with and neglected that I was chasing down multiple problems at a time for a while. The previous owner had messed with the throttle stop screw and TPS so I had to re-adjust my TPS using trial and error only, a process that took several steps over multiple days. HINT: DO NOT MESS WITH THE TPS UNLESS YOU HAVE GOOD REASON TO DO SO!

Conor
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EmporerZombie
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Woodie and Conor: Thanks for the replies! That's good information and I'll try that the next opportunity I get.

In the Chilton's manual it lists the sensor to check as the Manifold Air Temperature Sensor (also shortens it to MAT), which is located inside the air filter compartment. It was suggested to me to just replace it, but I hate to buy a new one and find out it's not the problem. If I did that for everything, I'd basically have a brand new car that doesn't run! Lol
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Memphis metro


Your Chiltons is correct. For a 90 model metro you have a mat sensor. Manifold air temp sensor. The resistance of the sensor changes with the temperature. Did you verify the resistance was correct for the temp at the time tested? Has this code reappeared? Any other codes? Have you done a compression test on the engine?
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dayle1960
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Fastest Hampster EVER

I'm leaning towards the compression numbers being low. Yes, if you change out the spark plugs it will run well for a while but they will get fouled up again due to bad things being thrown into the combustion chamber via worn rings or burned valves.

Please do a compression test. It is quick, painless and free if you have a tester. It will quickly give you an idea if the motor needs to be worked upon or if you need to spend your time trying to chase down the cause of the problem elsewhere.
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Woodie
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There is no such thing as a MAT sensor on any Metro. You can choose between Intake Air Temperature or Manifold Absolute Pressure sensors.
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Memphis metro


During the early years of this fuel injection technology they changed the names of things quite a bit. What was called a mat sensor in 90 was in later years called a iat sensor.


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EmporerZombie
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Big Rhino: I did indeed verify the resistance was correct for the ambient temp, according to the chart in the Chiltons. I haven't done a compression test, but if after I clean the grounds it still acts up that'll be the first thing I do. The thing that gets me about that is why it would occasionally run smooth, for both short and long periods, after I reset the computer. If the compression is low, wouldn't it be consistently running badly?

I've checked the codes three times, and two of the three times it has appeared. In ignorance I didn't watch the codes long enough to see if there were others. The time I checked the codes and found that they were clear, the engine was acting up at the time. Since then I've been pulling the fuse and resetting the computer in an attempt to get it to drive better.

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EmporerZombie
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I'm on my way out to check the grounds right now. I'll let you know what I found. Thanks again for the help, everyone!
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EmporerZombie
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Alright, so I pulled off the ground wires and cleaned them up. I wouldn't say they looked corroded or really that dirty. The terminal wasn't shiny, but didn't look too bad. Nevertheless, I took some sand paper to it, to the block, and polished up the bolt.

I also ran the compression test. Each cylinder measured around 150 psi, with a variance of less than 5 psi.

The plugs looked ok. They weren't gunked up or all burnt. This is the second set since this problem started happening, and the first set didn't look bad either.

I did notice on the way home it ran great, but then again that's what it always does after I work on it. The real test will come tomorrow when I start it up and take it around town. I'll know in the next week if cleaning the ground improved things at all.

I will say this, it was running rough when I first started it, and after driving it down the road a few hundred feet I got out and upped the idle speed. See, when it was really acting up several weeks ago I had to lower the idle speed because the computer upped it in an attempt to compensate. It was really racing, and making it hard to get in gear. As long as I've had this car I've messed with the idle speed. I usually adjust it in the spring and fall to get it in the sweet spot. Now, I tried adjusting the idle speed weeks ago to see if it had anything to do with that, and found that to get it to run around the 7-800 RPM it suggests, I had to turn it almost all the way down.
Basically, the very fact that I had to up the idle speed gives me hope that the ground was the problem and that it's back to normal now.

Edited by EmporerZombie, May 26 2013, 10:24 PM.
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EmporerZombie
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Woodie: I want to say THANK YOU for posting that pic of where to find the ground wires! That helped tremendously.
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cwatkin


Yeah, my grounds didn't look that bad either but it made a big difference when I cleaned them. Did you put anything there to make sure they don't corrode again?

Conor
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Woodie
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That's the most valuable picture on the Internet. Big thanks to the person who provided it. (used to know who that is, but I'm drawing a blank right now)
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