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1997 Geo Metro idle surge
Topic Started: Oct 20 2010, 02:30 PM (2,596 Views)
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A friend of mine has a 1997 Geo 3 door hatch and is having idle surging problems with it. He's had a mechanic replace what the mechanic thought was wrong which included the ECU and some other odds and ends.

I've heard this is a common problem for Metro's but all the fixes I've seen were for 1994 and older models.

The surges are completely random, cold weather, warm weather, etc. He started it for me for a couple minutes and it ran fine but when he left a couple hours later to go home it did it.

Any ideas?
Edited by FastasEF, Oct 20 2010, 02:31 PM.
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Johnny Mullet
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Fear the Mullet

You have a vacuum leak somewhere. Inspect/replace all bad lines. There is one directly under the throttle cable attachment that usually goes first.
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:+1 surging is almost always due to vacuum leaks, $10 worth of vacuum line from autozone or the like will replace all the lines under the hood, just do them one at a time so you don't get confused. There's a vacuum diagram on the hood that may help as well. Surging is likely to appear only once the engine has warmed up since it goes into closed loop, running fuel trim by sensors instead of automatic warm up, not always true, but typical. A quick way to check, if you have a vacuum gauge, <$20 at harbor freight tools, tap it into the MAP sensor line(sensor on the passenger side firewall) you should have 20"Hg and steady vacuum if all lines are present/working. Your friend's mechanic is not very good if he replaced the ECU thinking it would solve the problem... big waste of time and money. The other 2 possibilities (much less likely) are the TPS on the passenger side of the throttle body (it may need to be adjusted) or the IAC valve on the drivers side of the throttle body may be malfunctioning, but by far the most likely is a bad/missing vacuum line.
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As a side note, it seems more and more common that both mechanics and shop manuals suggest replacing parts before doing proper testing regimens. mwebb is right to be testing with a scope, ALL mechanics should have one if they're running a repair business. My grandfather was demo'ing scopes to shops back in the 60's and 70's. Knowing what to look for on a scope attached to the right place on a car can tell you exactly what's happening and where without replacing anything. Proper testing of the issue on this car with a simple vacuum gauge should have been an initial test, and the mechanic should have known that if he's had any real experience REPAIRING cars (not just switching parts out till its miraculously fixed) If it turns out to be a vacuum line, your friend should go back to the shop and ask for his money back on the ECU since his was almost certainly fine (I'm sure the mechanic didn't test the ecu before he switched it out) If he refuses, threaten to report him to the BBB and local chamber of commerce, do it if he continues to refuse. There's no reason why bad shop policies should be allowed to perpetuate in the manner which they have. As an example, I was quoted $2000 for a repair which took me 4 hours to do by myself with hand tools, it would have taken half that time in a shop with a lift and air tools and parts/fluids cost ~$200.
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Bad Bent
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Facetious Educated Donkey

Welcome to the forum, FastasEF! :coffee

The hoses are the first to go and after replacing the vacuum lines, granted it still does it, I might suggest testing for leaks by spraying carburetor cleaner or starter fluid on the intake manifold and Throttle Body where leaks might occur. this is all Do It Yourself. :thumb
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