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Part throttle surging 
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Joined: Sun Aug 04, 2013 11:36 am
Posts: 17
Post Part throttle surging
My galant VR4 has been giving me some troubles for awhile. Drive fine at WOT but at low throttle inputs it bucks and surges. On cold starts is idles at like 2000 RPM and surges but once it gets warm it idles nicely at 1000 RPM.

So far I have:
Checked for leaks. Gets to 20psi on the leak tester and then leaks down slowly.
Replaced the plugs
Replaced the plug wires
Replaced the throttle body and IAC
Adjusted the BISS
Replaced the Coil
Replaced the knock sensor
Pinned out the TPS and it was okay
Replaced the CAS
Went to another 1g MAF
Pinned out the MAF connector
Rewired the Idle Switch
Checked compression (its good)
Checked Fuel Pressure (its good)

Then I found rust in my fuel tank so I:
Got the tank blasted/cleaned
Replaced the fuel filter
Replaced the Injectors because this were full of rust(2G 550s)
Replaced the fuel pump
Replaced the fuel pressure regulator

I am running out of ideas. I have never taken any of my cars to a shop before but I am considering dropping it off at Road///Race Engineering at this point

My gut feelings are:

1. My replacement 1g MAF was also bad

2. Fucking 02 sensor is bad. Last time I had TMO logging it looked like it was stuck lean BUT I figured it was because the sampling rate was slow. BUT the fuel trims looked all in place and this doesnt make sense

3. The IAC is bad even though i pinned it out and it reads okay....

I am a fucking Mechanical Engineer, I calibrate cars for a fucking living, and I can't fucking figure this out. I am super aggravated. I just want to fucking drive and race this car.

Last edited by CAFIFTY on Wed Oct 09, 2013 11:23 am, edited 1 time in total.

Sun Sep 15, 2013 9:23 pm
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Joined: Tue May 22, 2007 6:46 pm
Posts: 2848
Location: La Palma, OC
Post Re: Part throttle surging
Check the coolant temp sensor.

99 GSX - 296.5 AWHP

I'm assuming you all have guns and crack!

Sun Sep 15, 2013 9:26 pm

Joined: Sun Aug 04, 2013 11:36 am
Posts: 17
Post Re: Part throttle surging
Yeah i was thinking about that today also.

Last time I logged stuff. ECT was reading correctly in TMO but was reading 120 degrees higher when viewing it TunerPro RT. Seems to be reading correctly in the dash though and the fans kick on and off.

Thanks for the quick response.

Still highly considering paying someone to figure this out. Is Road///Race Engineering my best bet?

PSS the car is stock

Sun Sep 15, 2013 9:29 pm
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Joined: Thu Oct 13, 2011 11:35 pm
Posts: 815
Post Re: Part throttle surging
Remove all your emission crap. Block of egr

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1990 tsi (Fwd) almost built
1991 tsi (awd auto) bone stock. dd when i get it to run
1991 tsi awd (stock) future build

Mon Sep 16, 2013 8:13 am
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Joined: Mon Aug 10, 2009 9:57 am
Posts: 1077
Location: Ontario, CA [IE]
Post Re: Part throttle surging
I second checking the coolant temp sensor, it can make the car hard to start and do other weird things. The ecu uses a different sensor than the temp gauge in the cluster. The fans run off a thermo switch that's plumbed into the radiator, below the passenger fan (for a 1G). Good luck and let us know what it was when you figure it out; it's gotta be something simple!

1992 Tsi
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Mon Sep 16, 2013 5:17 pm
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Joined: Sun Aug 04, 2013 11:36 am
Posts: 17
Post Re: Part throttle surging
I replaced the coolant temp sensor with a brand new one and its still surging.
I also replaced the 02 sensor and the TPS sensor. Still doing it.

Ordered a logger cable from and waiting to get that. Turned out my new laptop doesnt have the com port my old toughbook did so i cant use the cable i made awhile back :bang:

Another note. I noticed the when the TPS sensor is unplugged the car runs exactly the same as when its plugged in (shitty)...Thinking this might be the issue. Need to figure out the pin out of the TPS sensor. I guess pin 1 (green) should read 5v.

To top it all off when troubleshooting my engine just died and smoke started to come out of the ECU. Took it out and turns out the legendary caps decided to take a shit. I have another ECU but was so disgusted with everything that i decided to take a break.

I am really kicking myself for buying this thing.

Tue Oct 08, 2013 2:41 pm

Joined: Sun Aug 04, 2013 11:36 am
Posts: 17
Post Re: Part throttle surging
Starting to think its the MAF even though i replaced it. Anyone have a known good maf

Wed Oct 09, 2013 11:27 am
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