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SURGING IDLE: IAC or Vacuum Leak?; Need Diagnostic Help
Topic Started: Jul 21 2012, 02:37 PM (6,396 Views)
GeoZone
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View video here: http://www.youtube.com/watch?v=0pgyWN-ECbs




I have a 93 1.0L XFi that has a surging idle. Basically, what happens is after it warms up, and I let off the accelerator, I get about five surges before the idle settles in. According to SNOWFISH here: http://geometroforum.com/topic/4804867/1/ ,

"A corrupt IAC can be one cause of high idle and or surging idle. If you can blow air through the hoses, with your mouth, not compressed air, the the IAC needs attention." I followed the IAC repair thread and when I blew through the hoses I found that I could blow through the top but not the bottom. When I took the IAC apart I did not find that the spring was damaged in the IAC, so I put it all back together with new hoses and back on the car and still have the surging idle.

When I leave the top hose connected to the IAC but disconnect it from the little canister thing below the air cleaner I hear a sucking noise, then putt putt putt putt putt as the idle surges. If I plug the hose with a thumb, it settles down.

Is my IAC bad or is it something else?

According to MCMANCUSO, here - http://geometroforum.com/topic/4040345/2/

"The IAC is the thing with a hose running up to the air cleaner housing from the bottom. If you plug that hose and the RPM drops to ~750 then you've got another vacuum leak, if you plug it and it drops to ~300RPM(almost stalls) then you've got a bad IAC.

A working IAC should keep the RPM around 650-750, and when you plug the hose it should drop to ~300, if its not working(stuck full open) it will be letting way too much air in, but when plugged will correctly drop the RPM too low(~300RPM) if it only drops to normal, then you've got a leak letting air in somewhere else."

I'm not sure if he's saying to diconnect from the air cleaner side and plug, or disconnect from the IAC side and plug - I'm guessing air cleaner side. If so, then I think I might have a vacuum leak. But where? How do I find it. :hmm
Edited by GeoZone, Jul 21 2012, 03:30 PM.
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snowfish
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Basic GearHead

I would say that your IAC is working fine. :thumb Little to no change when you hold your finger over the hose. ^o) Another way, to test, would be to remove the air cleaner lid & hold your finger over the IAC port. Removing the hose at the silencer, like you did, does the same thing. Great job! :rocker

The thumping sound is the IAC opening & closing. It's attempting to control the idle. :gamerz

Has to be another vacuum leak some place. :news

If the vacuum lines have not been replaced, to your knowledge, less than a ten dollar bill should get you new ones. :deal Then we've eliminated one variable from the equation.

The quest continues............... :news
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Coche Blanco
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:gp
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GeoFlyer
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What's weird about this is that the surging stops. Mine had a vacuum leak in the throttle body gasket that caused surging idle... but it didn't happen immediately on engine startup... it would go into high idle... and when the high idle was over, it would go into this surge pattern and keep doing it whenever the throttle was closed. Good luck finding the problem!
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crankcase


Another place to investigate is the brake booster line. It gets stopped up, so try looking for blockage. There should be a vacuum on that line to help you be able to press the brake pedal down. There is also an internal one way valve that helps keep some vacuum on the line if the engine dies. Again it is inside the line, so if you need to replace the line, try to retrieve it for reuse.
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96Geoman


Found this on Google...

engine surges at stop sign

"What do I need to adjust or replace on my 93 metro 1.0 5speed metro. At operating temps engine surges up and down when you pull up to a stop sign. She also idles up high in cold weather. Could use any help."

Solved: "I repaired my problem, cleaned the EGR valve port thru the intake and fixed the problem and also replaced the pcv valve run like a new car."

http://autoforum.classifieds1000.com/Geo-Metro/engine_surges_at_stop_sign
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DesmondGhostRider
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Another thing to do would be to remove all the vac lines and using an air compressor to blow it all out.

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GeoZone
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Wow, sounds like a lot of variables. I'm away from the geo for a few days so I'll have to try all this stuff when I get back. Thank you everyone for all the great ideas. I would say that it is very much like what 96Geoman found -surging at a stop sign. I have replaced a few hoses so I guess my first step is to replace 'em all. Gonna have to at some point anyway.
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Khaney01
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Hillbilly at large

Sounds like the exact problem I am having with my '93xfi. Surges a few times before coming to a high idle then slowly dropping to near normal idle. Only does it when warm. I got it to come down close to normal by cleaning the egr ports in the intake. Iac is in good shape, just checked it. No response to carb cleaner on the vac lines.
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GeoZone
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I've been meaning to research the EGR thing. Not sure how to do it but sounds like it might need to get cleaned. I'm still dealing with mine, haven't had the time to mess with it. I had it into the shop for an oil change and free vehicle inspection or whatever and they did a vac test and said "no leak -$89 for a diagnostic". Yeah, no.
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crankcase


If you work the EGR diaphram by hand and it doesn't change your idle, it's probably blocked.
The EGR port starts on exhuast manifold and goes up into throttle body.
The passage is often blocked on many cars when we Metro Heads get them.
There is a thread around here somewhere on the procedure.
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GeoZone
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crankcase
Aug 15 2012, 12:33 AM
If you work the EGR diaphram by hand and it doesn't change your idle, it's probably blocked.
The EGR port starts on exhuast manifold and goes up into throttle body.
The passage is often blocked on many cars when we Metro Heads get them.
There is a thread around here somewhere on the procedure.
:coffee OK thanks I will definitely make that #1 thing to check out on my list.
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Khaney01
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Hillbilly at large

I took my IAC apart yesterday evening and it was fine,so I cleaned it really well with ether. Put it all back together and it ran great, no surge and idle was normal. I decided to check the oil after coming back from the test drive and noticed I had not plugged the wiring back in. I plugged it in and celebrated with a beverage of a refreshing nature. This morning, first stop sign I come to, the surge is back. I whip into a nearby parking lot and unplugged the wire from the IAC. Been driving it for almost 3hours now with no surge and normal idle. I have no clue what this means but, figured i'd pass it along to you.
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snowfish
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Basic GearHead

Man, you are so close to perfect it's not funny! :rocker Congrats on testing, proving, and eliminated that the IAC is the problem. :thumb

It has to be that your TPS is just slightly out of adjustment. :hmm

I bet just a slight clockwise rotation, of the TPS, will clear this up. :gamerz

Entire procedure can be found in your manual. And much discussion/procedures can be found here.

http://geometroforum.com/topic/1341780/1/

If, you're spooky, about fiddling with the TPS, just mark where it is now. You can always put it back. :cheers
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GeoZone
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ahaa - more stuff for me to try. MAYBE I can get to it this weekend. Have been driving my work truck for out of town business so much I haven't seen the Geo for awhile - it sits in the company parking lot very lonely.
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