unstable RPM's - page 1 - Troubleshooting - VWDiesel.net The IDI, TDI, and mTDI source.

• unstable RPM's by wdkingery on 20 Aug, 2011 16:50
• Captain Ignorant put an oil pan gasket only to find out it was the oil pressure sensor!  
  
  C ar is doing a slight surge now.. Put a new fuel filter but it didn't help. It's slightly off idle.it will kinda stop accelerating for a second then kinda take off. If I mash it alittle more it won't do it
• #1 by nathan_b on 21 Aug, 2011 01:29
• throttle cable too tight?
  
  
• #2 by wdkingery on 21 Aug, 2011 10:27
• No plenty of play there
• #3 by bajacalal on 21 Aug, 2011 11:40
• To start with, make sure it's not ingesting its own oil, either from the turbo (if so equipped) or your PCV system, the later cars had the upgraded PCV and and valve cover baffle so consider the upgrade if it doesn't have these.
  
  Have any screws on the injection pump been turned?
  
  Mine also does this from time to time, where it sticks at a higher idle than where it should be (but it's nothing near a full blown run away). A dose of diesel fuel system cleaner seems to make it go away for a few months so my guess is that something is getting gummed up in there.
• #4 by wdkingery on 21 Aug, 2011 13:05
• Yes we must be on the right track. My idle can stick high to.. I've been putting all kinds of crap in the tank so who knows. It does alittle low speed buck at times too, and the diesel cleaner had cleared that up. I'm thinkin its related to the cold start.
  Oh, and yes i've done dicked with all the screws on my pump i've actually got th. Fuel screw turned down past where it came..
• #5 by ORCoaster on 21 Aug, 2011 14:03
• Hey all that "crap" you have been throwing in the tank is doing your motor good.  I get that surge at idle after a long run on the highway too.  If I look at the IP gauge it drifts a bit.  A few pounds at most.  If I get out and look I see air in the lines.  Race it a time or two and they go away.  Think it might be time to pull the connections at the fuel filter and smooth them out and heat them up till they turn blue.  That should get rid of my problem.  May do the same for you. 
  
  And turning the screws in and out is considered "tuning" and some people charge 100 an hour for that.  Some charge about the same for the term you used as well. 
  
  
• #6 by wdkingery on 21 Aug, 2011 20:03
• i made a video but the sound turned out horrible.
  
  what i found is that i can hold the gas pedal down slightly, and it will act like a obd-1 model honda with a vacuum leak... up and down rpm, very constant, stable, up and down, up and down.. then it will eventually break free and run up a good bit in RPM.
  
  do you think having the fuel screw turned out too far will do this? but it didn't do this for the first 400 miles after i turned my smoke screen back out
  
  EDIT: altho i got 46.7 MPG's last go round, my fuel gauge was reading waay high.. like i had barely used a quarter of a tank, but been 223 miles.. normally i break the 3/4 mark at 165ish miles.. and i heard a bearin squall like hell the other day after i fired it up. alternator?
  
  but it does it a lot worse when it's cold.. it actually becomes a buckin then
  
• #7 by R.O.R-2.0 on 22 Aug, 2011 13:32
• Quote from: wdkingery on 21 Aug, 2011 20:03

  i made a video but the sound turned out horrible.
  
  what i found is that i can hold the gas pedal down slightly, and it will act like a obd-1 model honda with a vacuum leak... up and down rpm, very constant, stable, up and down, up and down.. then it will eventually break free and run up a good bit in RPM.
  
  do you think having the fuel screw turned out too far will do this? but it didn't do this for the first 400 miles after i turned my smoke screen back out
  
  EDIT: altho i got 46.7 MPG's last go round, my fuel gauge was reading waay high.. like i had barely used a quarter of a tank, but been 223 miles.. normally i break the 3/4 mark at 165ish miles.. and i heard a bearin squall like hell the other day after i fired it up. alternator?
  
  but it does it a lot worse when it's cold.. it actually becomes a buckin then
  
  

  
  bearing could be the alternator, or more likely, the timing belt tensioner..
• #8 by wdkingery on 30 Aug, 2011 14:00
• it appears my timin had slid retarded a tad
• #9 by ORCoaster on 30 Aug, 2011 21:08
• And you paid the price of 45.3 mpg for it.  How did that happen?  Or was it the rebuild and reinstall that caught you?
• #10 by wdkingery on 31 Aug, 2011 06:37
• You know I don't know what happened! I don't think it was the reinstall. I don't know what it was.. Just don't know. Have to wait another 300 miles to see if it's better
• #11 by wdkingery on 31 Aug, 2011 16:34
• yeah it must have been where things weren't right under the hood, cause me and wifey went to the beach today.. tooled around for a little while then drove home, 280 miles.. got'er done in 5.22 gallons; 52.4 mpg! so i think i got it back right. and that was on straight diesel; wish i had added some wax/2 stroke to it.. coulda got like 54
  
  and we had some traffic waitin to go thru the tunnel; 20 minutes of stop and go.. I HATE STOP AND GO. makes me nervous cause my car gets right hot before the fan kicks in, and that only helps but so much.
  
  idle still aint' right tho
• #12 by ORCoaster on 31 Aug, 2011 19:32
• My idle is messing with me too.  I tried to set it different with a tweak, and I mean 1/16th of a turn of the fuel screw and I lost my extra power needed for the extended hills that seem to rob my car of momentum.  Once it got down to 63 I had no more pedal and was force to do a lot of dropping to 4th.  So my mileage suffered for it.  52?  now I am really going to have to think on the increase the mileage game.  You are again ahead of me.  Maybe the new paint I plan for this weekend will give me the coefficient of friction I need.  The body kit may as well.   
• #13 by R.O.R-2.0 on 31 Aug, 2011 22:03
• i doubt the body kit will even affect the mileage, or if it does, be very minimal..
  
  its not like you are making it any easier for the engine to get air in, or out of it, and thats where the efficiency comes from..
  
  getting rid of that horrid toilet bowl, and getting a better intake setup.. that 1.25" snorkel is pretty much a joke air intake..
  
  i have a mk1 header that i had on my diesel, helped mileage a bit.. i have no use for it.. pm me if you have any interest in it..
  
  (its the header, and flex joint, just take your stock stuff off, and weld this stuff on.. i may even be persuaded to install it for you if you come to me)
• #14 by wdkingery on 01 Sep, 2011 05:07
• Well you gotta remember I'm 3% high too, so you are probably actually higher
  
  Plus I never ever downshift, so you must have some hills I dont