Romps on startup

Sanborn

New member
Joined
Sep 20, 2020
Location
Ohio
TDI
2002 jetta
2002 tdi 230k miles. Automatic.

Romps shortly after startup. (Does not hesitate to start though).

Rpms jump up/down around 100 rpm ... Like some of the John deere/5.9 Cummins engines do on cold start. Start engine, idles smooth for 3-4 seconds... Then starts romping. Will stop after 30 seconds to a minute and be fine(temp related?). No power complaints.

If you unhook vacuum line to EGR valve, it stops.

If you unhook vacuum line to turbo actuator, it stops.

If you unplug MAF sensor it stops.

If you run EGR test(engine running), it chokes engine down and even stalled it once.

EGR desired and actual appear to be following each other.

I removed turbo outlet (clogged catalyst?) And it almost got worse! (Doesn't make any sense)

I took inlet boot off egr valve...the EGR cycles on and off every second at idle and this is when it's romping, it seems like.

Removed EGR valve and looked in intake... 3/16" or so of buildup. I cleaned it 2-3 years ago. (25k miles? Guessing).

We did change the turbo recently due to internal oil leak, but this problem was present before that.

Anyone ever run across this?

IQ is 6 at idle? I think...can't remember 100% (if doesn't sound right I'll look again).


Again, runs fine after intial start...also starts fine the rest of the day unless it cools all the way off. Engine temperature does seem to be a factor. Frustrating because you only get so many starts per day to diagnose it.....I keep getting the feeling that it's EGR related...but?????

Unplugged coolant temp sensor..no change.
 

jmodge

Veteran Member
Joined
Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
Coolant temp sensor on the head, I take it you unplugged the one on the radiator ?
 

jmodge

Veteran Member
Joined
Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
Check the temp in vcds from cold start to warm up to see if it is working. That’s the one that does engine controls. I think the other only controls cooling fans, I could be mistaken but I don’t think the radiator sensor shows on vcds
 

jmodge

Veteran Member
Joined
Jun 18, 2015
Location
Greenville, MI
TDI
2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
You probably won’t notice a change by unplugging it because either way it is not working c
 

Sanborn

New member
Joined
Sep 20, 2020
Location
Ohio
TDI
2002 jetta
I'll try to check again tonight, but thought it read 20c just sitting there
 
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