General First start up Idle surge 1G

[all black 4G63]

hello,
I have read through a lot of post about idle surge, but my test are not bringing me to isolate the cause.

This is the first time this engine has ran after a full rebuild. The CAMs are: Intake 264 and Exh 272 HKS.

The ECM is 92 AWD 4G63T (stock)

The IAC is new (replaced) and the TPS is replaced. The BISS screw is fully seated at the moment. The IGN Timing is not set accurately due to high idle.

I have checked for vacuum leaks by disconnecting the BOV vacuum hose, fuel pressure regulator hose and applying 19" Hg with a Mighty VAC and all components hold. I also disconnected the PCV hose and plugged the port with no change. I can't see any leaks with the IC piping or any thing else, unless the vacuum ports at the intake are leaking or injectors?

the video in the youtube link below shows DRB data while the surge is occuring.

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Any thoughts?

Thank you for your support.

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[1990TSIAWDTALON]

Can you turn the idle stop switch out so the throttle closes more? It sounds like the ECU is doing its thing cutting fuel above 1500 then refiring the injectors.
Initially set the BISS screw 2 turns out and work from there.
Speed density, MAF, log while it is surging? I'm sorry we aren't all as good with every alternate tuning method. I am used to Link. My fault.
The good thing is, it won't go anywhere without brakes......

 

[all black 4G63]

Hi, thank you for the replay.

The ECM is stock ECMLINK is not installed at the moment. I do not think it is possible to obtain a log with DRB.

I have removed the throttle body prior to running the engine and cleaned it. I can assure that the throttle blade is fully closed. However, I have another throttle body laying around I can just swap it to see if the surge changes.

I forgot to mention that when the MAF sensor is unplugged the surge stops, but the engine runs poorly. I'm not sure if that indicates anything?

I do have a DSMLINK ECM on standby. It is brand new out of the box, can I just plug it in and start the car without any initial calibration change?

Thank you
Anthony

 

[Lucky13]

Do you know when the last time your ECU was looked at/repaired for cap damage? I chased surge for a long time until I was able to diagnose that the ECU wasn't able to control the ISC and needed to be repaired.

 

[Vegas Smith]

Hmm, I suspect there is a lot going on here. I wouldn’t be surprised if it had a bad maf and some vacuum leaks etc. While we could figure this out without ecmlink it could take a long time. Ecmlink can just plug right in if the car is stock. Make sure software and firmware are updated and post a short log.

 

[all black 4G63]

Thank you for the replay.

The harness, ECM and valve body were taken off of a parts car (92 TSI) which exhibited the same surge. The MAF from that vehicle was not used, so we can rule that out.

I have replaced everything on the valve body, which leaves the ECM and wiring left I suppose.

I appreciate the assistance with this. I do have another ECM for this vehicle that I can easily swap. At least this will tell me if the ECM is the issue.

If the swapping ECMs does not help I will attempt to use my new ECMLINK ECM and capture a log. I just am a little hesitate as I have never used or even seen ECMLINK. I suppose a little reading and ill be able to figure it out.

Thank you

 

[all black 4G63]

Do you know when the last time your ECU was looked at/repaired for cap damage? I chased surge for a long time until I was able to diagnose that the ECU wasn't able to control the ISC and needed to be repaired.

Thank you, I have another ECM that I will swap as a quick test. I will follow up.

 

[all black 4G63]

I forgot to mention that the O2 sensor voltage is zero the whole time. I suspect a possible sensor issue, but I don't think a fault O2 sensor will cause this surge?

 

[Vegas Smith]

I forgot to mention that the O2 sensor voltage is zero the whole time. I suspect a possible sensor issue, but I don't think a fault O2 sensor will cause this surge?

It could if the fuel trims are terribly out of whack.

 

[all black 4G63]

I will swap that first. I will follow up tomorrow.

Thank you!

 

[steve]

The harness, ECM and valve body were taken off of a parts car (92 TSI) which exhibited the same surge. The MAF from that vehicle was not used, so we can rule that out.

I have replaced everything on the valve body, which leaves the ECM and wiring left I suppose.

I assume you are talking about the throttle body when you say valve body. If you used the TB from another car that was surging I'm not surprised this one is even after cleaning it.
Most surging is caused by too much air reaching the intake manifold, you've checked for leaks from the outside (vacuum leaks) but what about leaks inside allowing air past the throttle plate?
There are several paths;

The normal TB butterfly needs to be fully closed and the factory seals it with a black coating on the plate around the edge.
The BISS screw controls the main bypass and primary adjustment. If yours is all the way in then the main passage is blocked and you must have other ways for idle air to get in.
The FIAV (Fast Idle Air Valve) provides additional air while the engine is warming up. It's coolant activated and the bypass closes as the coolant flowing through it reaches operating temp. These are known to stick with age. If you don't have coolant running to the TB the FIAV will be stuck open allowing air to bypass the TB butterfly.
The ISC (Idle Solenoid) is the ECU controlled bypass. The original metal can ISC are known to short out and blow the drivers in the ECU. If the ECU can't step the ISC pintel in and out then it will be left in some position between fully open and fully closed and the ECU will not be able to control the idle speed. You can measure the ISC coils to see if their shorted but you can't easily check the ECU drivers other than watching the ISC step in and out during ECU power up.

It doesn't take much air at all to cause the engine to idle high. With a bad/leaky PCV valve just opening the oil cap can change the idle speed.

 

[all black 4G63]

thank you for the information. I will double check the FIAV as I did not swap that yet. However, I did swap the ECM with a known good one and the surge is still there!

When the engine is initially started the RPM sets around 1900. I truly believe air is getting by. I have check external vacuum leaks so i'm assuming throttle body issue or IAC.

I began by holding the IAC in my hand when the key was turned on. I do feel a little movement, but not the same as my other 1G with no issues. So I scooped the good cars coils.

Is this photo, it is showing the WHITE wire (coil B1 control) probed at the IAC- this is known good KOEO (yellow trace)

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This photo is the same wire (coil B1) on the "bad" vehicle KOEO

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You can see I am missing the pulse to ground. However, I am not sure if this is even a problem because both vehicle are reaching battery voltage.

When the key is turned on (good vehicle) you can hear the IAC motor pulse. But when the key is turned on (bad vehicle) you do not hear the pulse.

Coils A1-A2 and B2 match the known good vehicle.

Does this look like an issue?

I will swap throttle bodys now to see if the FIAV is the issue. I will update

Thank you very much for the help.

 

[all black 4G63]

HOLY SHIT IT WAS THE FIAV!! I swapped the throttle body and it idles!
damn that thing must of been stuck wide open to premet 1900 RPM idle.

Thank you everyone on this site!!!! Shit where do I donate!!!

 

[Vegas Smith]

HOLY SHIT IT WAS THE FIAV!! I swapped the throttle body and it idles!
damn that thing must of been stuck wide open to premet 1900 RPM idle.

Thank you everyone on this site!!!! Shit where do I donate!!!

The site's donation link happens to be my Paypal address.

 

[all black 4G63]

what is procedure for adjusting that FIAV closed? is it clockwise or counter clockwise?

 

[Vegas Smith]

https://www.dsmtuners.com/threads/fiav-adjustment-disable.320951/

 

[steve]

With that scope trace I suspect you have a bad driver or open trace inside the ECU for your B1.
The ISC gets battery voltage on the two center pins which is fed to each of the four coils in the stepper motor and the ECU then pulls the coils low in sequence to cause it to step in or out.

A weak driver will have problems pulling the ECU side of the coil low and a bad or open trace won't pull it down at all. It's common for the corrosion from the capacitors leaking to eat into the circuit traces.

 

[all black 4G63]

Thanks, I will swap ECM's again and take another trace. Hopefully this info is useful to someone else diagnosing idle issues on these cars.
I will follow up after I swap.

 

[steve]

Your welcome.
I've assumed you were measuring at the ECU pin, if it was at the ISC then also check the continuity between the two points.

 

[all black 4G63]

Hi Steve,

Actually I had one lead at the IAC and another lead (chB) on the same circuit back probed at the ECM. The trace was identical. I did this to see if there was resistance in that circuit. Therefore, with those results, the circuit should be OK. I took the screen shot with that CH off.

Thank you for the info.

 

[all black 4G63]

I installed my other known good ECM today and the pulse is back and everything is working correctly. I did not save the capture, I Just wanted to update this post so that someone else with this problem will know a missing pulse to ground on each coil circuit during KOEO is a problem.

Thank you all for the support the vehicle is running great!
Anthony

 

[steve]

Send the bad ECU to the guys at ECMTuning and they can fix it up. I've been sending everyone that direction since I stopped repairing them.

 

[all black 4G63]

Yes, after I opened the ECM to inspect it i found it is actually a chipped ECM from the factory. (MD-626) I also realized it is a remanufactured or repaired ECM (it had a sticker that said do not open) I saw one transistor was replaced as well as some capacitors. However, the caps look to be slightly leaking. I will post photos.

 

[all black 4G63]

Yes, after I opened the ECM to inspect it i found it is actually a chipped ECM from the factory. (MD-626) I also realized it is a remanufactured or repaired ECM (it had a sticker that said do not open) I saw one transistor was replaced as well as some capacitors. However, the caps look to be slightly leaking. I will post photos.

Here are some photos of the ECM. What do you think?

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[92AWDHX40]

Doesn't look normal get that repaired send to ecmlink.