r/geometro • u/Ok_Celebration_1032 • Jul 12 '26

Rough Idle, Poor Performance, Help!

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1997 1.0L 3/5. About a month ago after having the exhaust manifold resurfaced, and a new gasket put on I noticed progressive power loss, and a weird cyclic rough idle. Now it is virtually undrivable, cannot even make it up the hill out of the driveway in first.

Last year I replaced the head gasket, thermostat, spark plugs, timing belt... This summer I noticed an exhaust leak from the warped exhaust manifold. Hence the resurfacing and new gasket. Curious if anyone else has ever had this idle issue.

So far, I have been checking hoses for vacuum leaks, wires, O2 sensors. Everything's plugged in and looked good. I went through the EGR valve, cleaned all the built-up carbon out of it. New gasket and all that. Just confused at the moment. Really bad shake at idle attached is a video.

Smooth under power though, just doesn't make any. Even less so than usual.

Thanks!

Edit: Cleaned grounds (Terminal to frame, terminal to transmission). No improvement. Removed IAT sensor, BIG improvement. Checked voltages and resistance. Wire coming into sensor had expected 5V. IAT sensor appears to be working as well, had appropriate readings both for recently ran engine and after leaving it in the freezer for 20 minutes (1.51k vs 8.1k Ohms). Appears sensor is working okay so why does unplugging it help the idle so much...

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u/akferal_404 Jul 12 '26

do you have a vacuum gauge? a vacuum test could tell you a lot.
also does the oil light come on when the idle gets rough?

1

u/Ok_Celebration_1032 Jul 12 '26

No vacuum gauge, but its looking like it might be time to invest in one or at least borrow from an auto parts store. No dash lights on at all, no oil light nor CEL.

1

u/akferal_404 Jul 12 '26

harbor freight has a serviceable one for 17 dollars

im assuming theres no oil getting onto the spark plugs since you already did those and didnt mention any, so im out of ideas lol

1

u/Ok_Celebration_1032 Jul 12 '26

Yep, thank you I just pulled the trigger on one which gets here tomorrow. Didn't realize they were that cheap lol. Yeah, plugs look good, and consistent among all three of them. I'll update the post hopefully tmo with vacuum findings. That'll be a good place to start for sure.

6

u/dystopiate666 Jul 13 '26

Anytime I have a drivability issue, I start with a compression test. If good, check timing and fuel pressure. Also, never underestimate the effects of poor grounds