98 NB erratic idle

[groovyIII]

Sometimes idle jumps up and down between 800 and 1200. Also when you let off and accelerate it jerks. If I turn key on and off it sometimes fixs it.

[Anony00GT]

Scan for codes, post anything you find.

Clean the throttle body and do a TB alignment with VCDS.

[groovyIII]

will do!

[blksabbath]

I"m dealing with a simillar issue. I had codes which point to vacuum leaks and MAF issues. Replaced the lines, got rid of a two codes and it ran better...but still had hicups. Cleaned the MAF, got better, but still not right. Ended up buying a new MAF because I was still on my original from 1998....amazingly. Putting that in as soon as it arrives. I did a TB cleaning not to long ago and the codes for that went away.

Anyways, all pretty simple things.

[groovyIII]

codes 172b,341,411,1582,121,131.

[Anony00GT]

Code definitions would make it a little easier to help.

Start with P0341. That's a cam sensor code. Could be a bad cam sensor, but more often than not it's flagged when the timing belt isn't properly lined up. What is the history on the car? Any work done recently? Check the timing and correct this code first.

Then verify that there are no vacuum leaks. Remove the throttle body, thoroughly clean it, re-install it, and perform a throttle body alignment with VCDS.

[groovyIII]

Just had a new water pump installed which involves removing the timing belt I believe.
Although the idle problem was there prior to the work done.

[filthy2.0]

Clean the throttle body and do a TB alignment with VCDS.

^ x2. start with the easy, cheap fix.

chasing the P1582/17990 code, the VAG-COM forum led me to the proper way to clean the throttle body.

the valve has to be able to rock backwards about 5 mm to the stop position molded into the throat. using carb/throttle cleaner, like gum-out, clean the throat, the valve plate, and all surfaces that make contact. think it's clean? clean it again. run your finger around inside and check for any residue that you can't easily see. especially clean the valve hinges (at 3 o'clock and 9 o'clock.)

now here's the really cool part. once it's mirror-shined, take a q-tip and dab a little motor oil on the hinges where the valve attaches to the throat. massage the valve backwards 5mm repeatedly. if you had a dirty throttle, you'll have a bit of resistance at first. keep rocking the valve backwards until it takes very little pressure to make it contact the stop. rock it forwards and backwards, adding dabs of motor oil as necessary. again, once you think it's lubed up, lube it again.

be patient and do a thorough job. those hinges have to be clean and able to move freely.

i don't know a lot about the technical ins and outs of the throttle, but evidently the ECM needs to use that 5mm backwards position as a baseline for setting the idle air mixture. according to bentley, it also allows the throttle to burn exhaust gas from the EGR/PCV/UFO-looking thingy on the valve cover - more efficiently.

my '97 ABA 8v was throwing code P1582 and P0506 (which has something to do with idle air control) , and after i cleaned the throttle the car cleared the codes on its own after a couple hours of driving. no further steps - like throttle body alignment - appear to be necessary at this point.

of course, YMMV. if, after cleaning, the car doesn't clear the codes on its own within a day, you'll have to figure out whatever mechanical steps to take next to make it happy.

[filthy2.0]

Just had a new water pump installed which involves removing the timing belt I believe.
Although the idle problem was there prior to the work done.

most likely unrelated.

for your own edification, since you had the work done, the water pump replacement doesn't require removal of the timing belt. the lower timing belt cover does have one bolt/nut that mounts to the water pump, but the cover doesn't even have to be removed.

most DIY'ers do both jobs at the same time since they're in the same neighborhood. at $70+/hour labor, though, greedier mechanics would probably prefer that you pay for both jobs separately.

curious as to what you paid someone else to the water pump, groovyIII. i just did both jobs myself, and parts from the dealer were expensive. i can't imagine tacking on the labor charge, shop fees, etc. you got all new hoses, too, i'm guessing?

[Anony00GT]

most likely unrelated.

for your own edification, since you had the work done, the water pump replacement doesn't require removal of the timing belt. the lower timing belt cover does have one bolt/nut that mounts to the water pump, but the cover doesn't even have to be removed.

most DIY'ers do both jobs at the same time since they're in the same neighborhood. at $70+/hour labor, though, greedier mechanics would probably prefer that you pay for both jobs separately.

curious as to what you paid someone else to the water pump, groovyIII. i just did both jobs myself, and parts from the dealer were expensive. i can't imagine tacking on the labor charge, shop fees, etc. you got all new hoses, too, i'm guessing?

Nope. This is a 2.0 Beetle. AEG engine. The water pump is driven by the timing belt. You're thinking of the ABA engine (A3 Golf/Jetta/Cabrio).

Given that he's got a P0341 and the timing belt was recently removed, it's probably a tooth off. IMO, that needs to be corrected before any other performance diagnosis is performed. Take it back to the shop that did the water pump.

[filthy2.0]

Nope. This is a 2.0 Beetle. AEG engine. The water pump is driven by the timing belt.

well, that's an unfortunate design.

You're thinking of the ABA engine (A3 Golf/Jetta/Cabrio).

indeed i am, and i apologize for any misinformation. it wasn't intentional.

Take it back to the shop that did the water pump.

what he said.

[groovyIII]

The problem was there before the water pump replacement!

[Anony00GT]

Try cleaning the TB and doing the adaptation with VCDS.

Regardless, the P0341 needs to be fixed.

[ekibobrut1]

I had a similar issue with my "98 Beetle. New plug wires solved my problem.