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VWDoc
VWDoc, Independent VW Shop owner
Category: VW
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Experience:  20 years of experience working with VW's. Independent European shop owner and technician.
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Volkswagen jetta 1.8t: have a low idle misfire,a couple pending

This answer was rated:

have a low idle misfire,a couple pending codes and 23-26% short term fuel trim

VWDoc :

Hello, I'm Jason. I will do my best to answer your question quickly and accurately using the information you have provided.

VWDoc :

Sure the code isn't a 2181?

VWDoc :

However, that would be secondary to the fuel trim issue

VWDoc :

you've got an intake leak, downstream of the MAF somewhere

VWDoc :

best course of action, if possible, is to have the intake smoke tested

VWDoc :

these have a lot of problems with the PCV systems deteriorating

Customer:

i am getting a torbo to throttle vale reduction code and misfire codes

VWDoc :

Boost deviation code......also check the diverter valve to see if it holds vacuum....

VWDoc :

I'll post a picture of it so you know what to look for

VWDoc :

That small nipple has vacuum running to it and should hold vacuum

VWDoc :

very common part to fail

Customer:

its a p1297 code

VWDoc :

but I have a feeling you have other leaks

VWDoc :

Ok, 1297.....you already replaced the sensor in the flange at the back of the head? If this code comes back, replace the thermostat, and when you have the old one out, poke your finger in the hole to see if the water pump impeller is broken at all

Customer:

how do i check if it is holding vaccum

Customer:

i replaced t stat already and cts

VWDoc :

best to have a vacuum pump handy to be sure. If it's not been replaced recently, they're problematic enough, that I would just swap with a new one

Customer:

didnt replace any sensor in back of head

VWDoc :

The CTS is green and fitted into the black plastic flange at the back (driver's side) of the head

VWDoc :

that's the one that fails, and will cause that 1297 code to come up also

VWDoc :

still, this won't cause the lean code

VWDoc :

smoke test is important here

Customer:

yes it was already green but i replaced also

VWDoc :

ok good

Customer:

had a 1297 code prior to all this

VWDoc :

ok, so likely dealing with at least 2 separate problems here

Customer:

also the large fan was not woking and the small fan only worked on high speed.replaced both fans and now all work as they should

VWDoc :

ok, pretty common also, at that age

Customer:

does the DV need to be oem?

VWDoc :

as long as it's Bosch, it will be fine

Customer:

i used denso platinum plugs

VWDoc :

For what it's worth, I will only use NGK PFR6Q plugs in these

VWDoc :

you can do an aftermarket DV, but they're pricey

VWDoc :

and not really necessary

VWDoc :

I have billet ones in my allroad, and Bosch in my TT

Customer:

do you recommend replacing the diverter valve at this time..

VWDoc :

that's a good start, but I have a strong feeling that a smoke test is going to be necessary

Customer:

i was trying to get the monitors ready for inspection and went 140 miles still 3 not readies...catalyst,evap,sec air

VWDoc :

what scan tool are you using?

Customer:

i have an autel and snapon

VWDoc :

a VW specific tool will allow you to run all tests without driving a single foot

VWDoc :

ok, snapon, in expert mode, you can do readiness.

VWDoc :

which Autel? The big DS708?

Customer:

not the big autel its a 805 maxdiag elite i believe

VWDoc :

Ok, that one won't do the readiness setting, but the snapon with Euro software will

Customer:

ok

Customer:

so your saying a smoke test to check for vac leak

VWDoc :

yep. I use mine literally every day. It's a must with these older turbo VW/Audi

Customer:

any chance a buildup of carbon on intake valves cuasing leaks

VWDoc :

nope

VWDoc :

well, I suppose there's a chance, but I work on hundreds of 1.8T cars and have never seen that be an issue

Customer:

ok thats good..but the Dv diverter can cause it

VWDoc :

when you look in the table of contents in that link, you won't find your engine code for the 1.8T Jetta. Use the AWP engine code. That's what you have

VWDoc :

they only show that code for the Beetle turbo in there

VWDoc :

DV can cause it, yes

Customer:

ok i will start with that and smoke test

VWDoc :

perfect.

VWDoc :

Let me know if I can help in the future.

Customer:

thank you for all the help..

VWDoc :

Again, I'm pretty darn familiar with these :-)

Customer:

i see

Customer:

thanks again

VWDoc :

sure thing

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