Hesitation,misfires 98 jetta tdi

Seems to be every month or so she'll be driving fine then bam, you can hold it to the floor just to stay at same rpm and occasionally go up a hair then back down like fuel is being restricted. Everytime I dump a crap ton of diesel kleen in the tank or In filter it seems to clear up for a while. Really not sure if it's bad diesel, injector nozzles worn? Moisture in the tank from cold weather or? She does have 287k and a stage 1 Malone tune. it does cause the check engine light to come on, always between 2-3k rpm she will just sit and occasionally take off like it should.

Videos are always helpful if possible. How long is this period of time where the car wont accelerate properly? Is it only for a few min while driving then gone after the car starts up the next time or will the issues be present for several days / repeatable?

Also how much is "a hair up then back down" 1000, 500 etc RPM? Possible that it could be bad fuel because you notice a difference after adding some sort of fuel additive, but not that likely because it would probably be driving like junk the whole time if it was an entire tank of bad fuel. Also nozzles arn't that intermittent, there is usually a consistent symptom that likely only will get worse if it was them.

Other possible rpm fluctuating causes could be TPS (throttle position sensor), fuel pick up from the tank being clogged up. Do a search for "tdi fuel pickup restriction" you will find some info (I also have a 97 jetta tdi so I know from experience).

The most helpful info would be either vagcom logs to see whats being reported by sensors, also like I said even a video while its happening would be a great starting point. I'm sure some of the more experienced guys will have some more insight.

diesel kleen isnt worth that much. diesel purge is what to use. <when needed. as far as a fuel conditioner, i prefer better than the power service. its ok, but there have been problems with it.
id say start with replacing all the vacuum lines, and go from there. its an easy place to find rough running, power missing. theres a short line inside the ECM that needs to be replaced, while doing this. i took mine to a shop, wasnt cheap, but well worth it.

i had almost forgot, probably best to replace your fuel filter, prime it is best. and the same for your air filter as well.

If the engine light came on, there is a code stored. First step is scan for codes and report what you find.

Generally less then 500 rpm, usually after running the diesel kleen she's good for a while it seemed, but after this last time after a day it's back to acting up.. Not cutting out or misfiring but almost no power or take off like before with a added knock noise on acceleration. Wondering if the injectors are on their last legs lol.. I'll have to go to the parts store tommorow and see what codes its throwing.

the diesel kleen may be *rather mild(compared to a good system cleaner) but its not a good idea to use a whole lot, like a whole bottle in one tank, after another. time after time can cause you problems. and right now your having problems. this may be a cause of problems. one question, if you look at your clear line, the opaque or clear line after fuel filter, and going into the pump. is there air in it?
using a whole lot of treatment like a whole bottle, or excess in a full tank is usually a lot once every 6months, to give you an idea. more can cause problems, like eating at your seals.

Cptnkush42zero said:

. it does cause the check engine light to come on, always between 2-3k rpm

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so in wondering it may seem you notice your CEL(^check engine light) come on, so are you saying it goes back off? just wondering on how you worded this, or it comes on, like you say, and some how goes back off??

It always went back off after about 5 times driving the car after that diesel kleen worked its way through a little. But this time it's back to stay it seems. I however did dump a whole jug of that stuff to like half a tank of fuel then topped the tank almost full. I've had to use the stuff every month damn near, was the only thing I found that fixed it. However I just fired it up and stepped on it a few times around the block and she was fine. Also seems to happen when it's damp outside or about to snow. There's also an ignition interlock device in the car... Maybe that's messing with it?

iluvmydiesels said:

one question, if you look at your clear line, the opaque or clear line after fuel filter, and going into the pump. is there air in it?

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i dont know if youve been reading the responses as i didnt hear a reply from you ^this-?

Cptnkush42zero said:

It always went back off after about 5 times driving the car after that diesel kleen worked its way through a little.

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so i hazy to what you mean here, the CEL light always went back off? is this what your saying above?? if so for one, if you try to get codes with the stock electronic(management) system(ECM and engine management i mean), the CEL light must stay on, or BE on to scan codes. if its off its not saved. unless you or a prev owner did -other modifications, im not immediately aware why the CEL would turn back off.

iluvmydiesels said:

id say start with replacing all the vacuum lines, and go from there.

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^a common recommendation and solution. wont necessarily solve yours, we wont know until all vac lines are working right. theres like at least 10 lines. i find it easier to suggest and a quik fix in cases. this would include as i posted above change and prime fuel filter, not a bad idea to put in a new (&good) air filter at the same time.