ALH--50 RPM surge at idle, increased fuel consumption

HBB

Member
Joined
Oct 17, 2014
Location
Seattle
TDI
1990 Syncro ALH, 2005 Golf BEW
I'm trying to diagnose a surge at idle that recently developed. Engine is an ALH with largely unknown history (poorly executed Vanagon swap that I've been improving). P/O put Race 520 nozzles in at some point, probably did not properly calibrate them. The IP might be getting a bit nosier, but it's hard to say for sure. The IP has been apart, the P/O swapped out the QA at some point. EGR has been deleted, no intake clogging, seems to be getting plenty of air. This engine is running off of an AHU ECU for some reason (P/O apparently found that easier to work with for the swap). RC II tune.

The engine had previously idled smoothly, rock steady at 903 RPM, but it's recently developed a surge at idle, seems to rev up to 930-40 or so, and then drop to 860ish. The surging is intermittent, on some cold starts it won't do it, or at least it's not as pronounced. Starts right up, no smoke except at WOT.

Just wrapped up a 150 mile trip, filled up at the start and the fuel gauge is already almost down the halfway mark, which is not normal. I usually get low 30's for MPG, which is pretty good for a Vanagon swap.

Fuel filter was recently replaced. No reason to suspect bad fuel, my PD BEW Golf gets fuel from the same station, and is running fine.

Timing is just a touch above the middle of the graph.

VCDS is showing 00550-Start of Injection Regulation 17-10 Control Difference Intermittent. I did get this code about a year ago, cleared it and it never came back.


IQ is bouncing around from 8.0-9.0 mg/str. I had it set at 7.9 if I recall correctly.

Specified SOI 4.2 BTDC, actual 2.9 BTDC.

Group 13: #1 2.99 #2 1.98 #3 1.74 (no #4 since it's an AHU ECU).

What's the best way to troubleshoot this? I'm not sure if it's the IP, nozzles, or injectors. I supposed it could also be an electrical problem with either the IP wiring or the 3rd injector as well.

Thanks in advance for the help.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Any other DTCs?

My ALH in the Vanagon will occasionally rev up to about 1100 rpms and just hang there for a bit when I first start it (cold). I always shut it down and re-start.

Considering it has never left me sitting beside the road and completed two long road trips, I don't worry about it. But, I do believe it is an electrical wiring issue associated with the conversion. It does throw the CEL... seems the code is 0226.... cannot remember for sure since it hasn't done it for a while. (it never idles below 903)

Edit: Seems my IQ is 3.2 ! Yours is too high (very lean, if I remember correctly)
 
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HBB

Member
Joined
Oct 17, 2014
Location
Seattle
TDI
1990 Syncro ALH, 2005 Golf BEW
Any other DTCs?
No, not that are relevant. I've excluded the normal DTC's I get due to not having the glow plug indicator and vehicle speed sensor hooked up.

Seems my IQ is 3.2 ! Yours is too high (very lean, if I remember correctly)
I appreciate the help Andy, but I'm not sure if I understand the relevance of your IQ setting. I'm running significantly larger nozzles than you on a more aggressive tune. At anything under 5 the smoke level is ridiculous. Doesn't seem like a useful comparison, but maybe I've misunderstood.

Also, I'm having a hard time understanding how the IQ setting could result in an irregular idle. I can definitely see an IQ setting that's way off resulting in stumbling going between a loaded condition and idle, but my understanding is that no matter what value you have in there, the ECU is only going to inject enough fuel to maintain 903 RPM's at idle.

I guess I can hammer it down to 3.2 and see what happens.
 

jokila

Vendor
Joined
Dec 3, 2004
Location
Houston, Texas
TDI
2003 Jetta GLS, Manual
No, not that are relevant. I've excluded the normal DTC's I get due to not having the glow plug indicator and vehicle speed sensor hooked up.
I appreciate the help Andy, but I'm not sure if I understand the relevance of your IQ setting. I'm running significantly larger nozzles than you on a more aggressive tune. At anything under 5 the smoke level is ridiculous. Doesn't seem like a useful comparison, but maybe I've misunderstood.
Also, I'm having a hard time understanding how the IQ setting could result in an irregular idle. I can definitely see an IQ setting that's way off resulting in stumbling going between a loaded condition and idle, but my understanding is that no matter what value you have in there, the ECU is only going to inject enough fuel to maintain 903 RPM's at idle.
I guess I can hammer it down to 3.2 and see what happens.
IQ can cause idling issues if it's set too low as well. Too rich and the engine will stumble at idle. Search the posts on hammer mod and there should be explanations.
 

HBB

Member
Joined
Oct 17, 2014
Location
Seattle
TDI
1990 Syncro ALH, 2005 Golf BEW
Anyone have any comments on the Group 13 values or the IQ jumping around?

I didn't even think that Group 13 would show values over/under 1.88, but I've got 2.99 on one cylinder.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
Anyone have any comments on the Group 13 values or the IQ jumping around?

I didn't even think that Group 13 would show values over/under 1.88, but I've got 2.99 on one cylinder.
Swap that injector with one from another cylinder and recheck. This assumes we're tnot talking about the #3 injector.
 
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