Problems with Geo Prizm; Rough idling and misc. issues?

quinnisaurusquinnisaurus Member Posts: 3
edited August 2016 in Chevrolet
Hello, so I've been having trouble with my car, a 1990 Geo Prizm with about 152,000 miles on it. There's a lot of weird things happening and I'm not sure if they're all related or not. First off, my car idles really rough, but only sometimes, usually at night, it seems. I've noticed that when it's idling rough, it gets worse if the lights are on and better if they're off, but still noticeable. In the daytime, it seems to run/idle fine. Either way, as soon as a I start accelerating, the shaking goes away. That's the first issue. Another one, after running the car for a while, maybe 15-45 mins, the oil light starts flickering in idle. It only flickers when I'm idling in drive, but goes away in neutral/park or when I accelerate. I just changed the oil maybe a week ago, and I didn't notice the light before the oil change. (Maybe I did something wrong?) Another issue, after the car has been sitting for a while, like overnight, when I start it up, a cloud of white smoke/steam comes out of the tailpipe. It's not a whole lot of smoke, but it's noticeable and doesn't smell like anything.

So those are the main issues. I've tried trouble shooting the problem myself, but no luck so far. I replaced the O2 Sensor, changed the oil and oil filter, changed the air filter, replaced the rotor and ordered a distributor cap. The spark plugs look good, but I'm planning on replacing those along with the wires soon.

My ideas were that maybe the alternator was having an issue. (Because of the headlights making idling worse) Or maybe a battery issue, but I've tried different batteries with no difference. Possibly an electrical short somewhere which seems unlikely to me but I'm not a professional. I was thinking from the smoke maybe there's a coolant leak that might be related to the bad oil pressure because of a blown gasket or something.

That's all I've got. I'm 17 and don't have a ton of money to take it to a shop to be looked at, so some advice would be very helpful. Thanks in advance!


  • 93tracker5spd93tracker5spd Member Posts: 194
    Hello! First let's address the idle issue. You didn't say which engine you have, but the issue is likely the same. These engines run a very tight air fuel mix at idle. First locate and pull the EGR valve, if you repost with the exact engine, I will tell you the location. You will see a rubberized clothe diaphragm from the back side of the apparatus, press close to the center and see if it moves, if not it is clogged with carbon. This is common with these engines, if the EGR is clogged the air flow way right behind it leading into the intake is almost always clogged as well. Sometimes the airway and not the valve is clogged. This is your rough idle. If all are open, then you could have a vacuum leak or bad vacuum routing, you will need to find a vacuum routing map for your engine to confirm that all lines are connected correctly. Insure by visual and by bending that all rubber vacuum lines are not chaffed, cracked, split, or otherwise damaged. These engines are very sensitive. Once you have gotten the idle corrected, we will address the other issues. However I am pretty sure that the other problems are related to the poor idle and will vanish once you have a good steady idle speed. Please re-post with exact engine and transmission so that I can help you further. Good luck.
  • quinnisaurusquinnisaurus Member Posts: 3
    Hi there, thanks for your reply! I'm relatively new to the car scene, but I believe my engine is a 1.6L MFI DOHC 4 cylinder. Is that the info you needed? It's an automatic transmission. I'll also attach an image of the sticker under my hood in case you need that info. I can't for the life of me find the valve, although I looked up what it looks like.
  • 93tracker5spd93tracker5spd Member Posts: 194
    Hello again! Here is a little diagram that should be helpful. Another way to test this system is to press the diaphragm with the engine running at idle, before removing the valve, and see if the engine stumbles or stalls, if it does the EGR system is working. Engine must be warmed up. And be very CAREFUL of moving engine parts, fan, belts, etc. And ware short sleeves, if you ware long hair, tie it back or put it down your shirt, ware eye protection! Safety first means many years of enjoying repairing your own vehicle.
    If the engine doesn't stumble or stall on this test, the EGR system is faulty. Clogged valve, or intake airway behind valve, bad solenoid, or leaking vacuum line. Let me know how it turns out and good luck!
  • 93tracker5spd93tracker5spd Member Posts: 194
    Oh, almost forgot, make sure to check that oil level often, at least once a week. Or if there is a leak, check it every day.
  • quinnisaurusquinnisaurus Member Posts: 3
    Sorry for the late reply, I've been busy with work and school. I looked for the egr valve but after not being able to find it, I took it to a shop to have someone show me where it was and it turns out my car doesn't have one, so that cannot be the issue. I did however change the alternator and the oil pressure switch and the lights/electrical problem along with the low oil pressure problem went away. The car still smokes white smoke sometimes when starting up and still idles sorta rough after I've been driving a while, depending on the situation. It seems like some nights the car gets tired and has trouble accelerating quickly. Any ideas what this could mean?
  • 93tracker5spd93tracker5spd Member Posts: 194
    Hello again. I could only find one reference to a Geo Prizm 1.6L with no EGR system, this guy has an idle problem also but along with many other issues, oil in his radiator, gas in his oil, etc. etc. So that does not help us narrow down your problem with idle. In this case, I'm sure your idle is causing all the other symptoms you describe. When an engine is idling rough already, and you add the strain of electrical drag from the alternator, it just drags the idle down even more. My next thing would be to check all the vacuum lines to make sure there is none leaking and they are all connected to the right ports. For this you will need a vacuum map. I checked the Suzuki listings for your engine, ( you know GEO was a joint venture between Japanese Suzuki, GM, and CAMI Motors of Canada), Suzuki made the engines. At any rate they list two 4A-FE engines, the one without the EGR system was used from 89-92, that covers yours. Suzuki still has parts houses operating, I would check with them for a vacuum map or manual for your model. could have a lot of helpful info on that rough idle. Good luck.
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