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7 Posts
Discussion Starter #1
Hi All

Looking for recommendations for a 'specialist' in St Albans area.

We have a 1996/97 LHD T4 2.5 Tdi ACV with turbo/power problems. Engine starts and runs ok, but lacks power - struggles uphill, and doesn't feel like the turbo is working.

Replaced MAF and 2 pin coolant sensor, checked N75 readings. Disconnected/reconnected MAF - no difference. Replaced all vacuum hoses with silicon pipes. Local garage say Actuator is faulty (not convinced by his diagnosis). He said there were 3 fault codes.

1. 2 pin coolant sensor (replaced)
2. N75 valve intermittant
3. Throttle position sensor intermittant.

I'm guessing it will need another VAGCOM check, and I'm hoping someone may be able to point me in the direction of someone who knows a bit about these beasts.


Premium Member
2,572 Posts
Originally Posted by hobbyhorse on the 2/1/2015

General rules for diagnosing low power on the 2.5 tdi:

Rule 1 Check the pump timing.

Rule 2 Check the pump timing properly.... (Vagcom, VCDS) visual checks of the timing marks are useless.

Rule 3 Whilst running software check for codes but don't take them as gospel, just a guide (they may be old).

Rule 4 Ignore any twit who sucks air through their teeth then tells you they think it's the turbo.

Rule 5 Check all the smallbore vac & pressure pipes.

Rule 6 Check for blocked catalytic converter.

Rule 7 See rule 1

This rule set will clear the majority of faults.

Full of Cr*p....
9,135 Posts
Did you replace MAF for a "genuine" Bosch one?
Pieberg(?) also make them, but have totally different curves for the output (and the cheapo ebay ones are known to be garbage!)

You can drive and monitor the readings from the MAF with VCDS (EVERYONE with a T4 should have this!....I have a 50 quid XP lappy, software and lead that sits under my rear passenger seat at all times!) and compare expected with actual results.
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