AHF: Normal starting behaviour?

[VAG Fan]

This question goes to all current or past drivers of a Mk 4 TDI (AHF engine, VE pump). It relates to normal/abnormal starting behaviour.

When starting my AHF, it always used to blip once to perhaps to 1000 rpm, and then settle immediately on 900 rpm idle. Winter, summer, cold engine, hot engine, no matter.

But lately, sometimes it does a quick and very hard rev-up (to at least 1500 rpm) and then settles at about 1100 rpm. It also runs very "clattery" and makes more smoke on start-up. Then after about a minute, it settles down to the normal 900 rpm. This happens only on a cool engine, but it does happen both on cool and hot days. I hate revving a freshly started cold engine, but I can't stop it from happening!

At other times, it's the usual, old behaviour. Swing, fire-up, and immediate idle at 900.

Suddenly I'm not sure what is really normal. And I'm confused because the starting behaviour has become sporadic.

My first point is a new coolant sensor, because the temperature gauge on the cluster has sporadically been falling to zero, and lately has mostly just been sitting at zero.

Any inputs welcome!

[Rudi46]

Hi
Also had this on a car, cant remember but think it was sorted with a Boost leak that was fixed.
Powersteering pump pulley chowed up the Plastic pipe coming from intercooler to Intake.
Just a thing to check, Happened 8 years ago so memory is failing me. But sure this resolved the issu

[VAG Fan]

Thanks for the heads-up, no harm in checking for boost leaks.
[Edit: so, which is the normal behaviour, and which is the abnormal one?]

[Tdi jetta 4 ever]

Start by doing a scan. And while you are there check the timing with vcds.

[VAG Fan]

The car is almost due for a cambelt service, which entails the timing, and Panic scans for faults anyway. I'll mention this to him.

[Cerro]

When my 2004 Jetta tdi. had done + - 260, 000 km I noticed that the temp gauge at times stayed on zero
A few weeks later the consumption just got bad.
The cause was a faulty coolant sensor.
Jetta is now on 383, 000 kms.
Its possible your car's coolant sensor is faulty.
Bought from Goldvagen, back then around R250 -
Hope you come right.

[VAG Fan]

Thanks for posting your experience, and welcome to the forum!

Yes, I've actually bought a temp sensor, just haven't come around to installing it.

Lately, the starting behaviour has changed once again. The engine no longer revs up abnormally, but now, runs lumpy for the first few seconds. Consumption, by the way, has remained good throughout.

Interesting about the mileage. Mine is also just past 260k.

[Tdi jetta 4 ever]

Thanks for posting your experience, and welcome to the forum!

Yes, I've actually bought a temp sensor, just haven't come around to installing it.

Lately, the starting behaviour has changed once again. The engine no longer revs up abnormally, but now, runs lumpy for the first few seconds. Consumption, by the way, has remained good throughout.

Interesting about the mileage. Mine is also just past 260k.

Mine also does that. More like a mis fire. I think its because of the cold. I checked the resistance of the glow plugs and they seemed fine to me. Maybe its time for new or refurbished injectors.