The Surge - in my 4.9, not Iraq...

[EldoRedo]

Folks,

Recently I have begun to notice my engine briefly surge a little bit when I'm going about 35-45 mph. It's as though I'm giving it just a bit more gas when I'm not. I've tried to watch the tach and today I think it hit about 1900. The event lasts just a few seconds, and then it's like nothing happened. It's a pretty mild phenomena but a little disturbing none-the-less. No codes are set. I checked the throtttle cables today for any interference and saw nothing obvious. Any thoughts?

Thanks!

[cadillac_al]

Does it happen when it's low on fuel? low on fuel and going down hill? My fuel gauge is a little irratic so I have to kind of guess how much gas is in it. Whenever it acts funny I head right to the gas station and problem goes away.

[carnut]

Depending on how the trans TV cable is adjusted 35 to 45 is when 4th gear engages. So, you could be feeling the transition from 3rd to 4th. Try driving at the same speeds with the gear shift in 3 to see if it goes away. If its gone, you might verify the TV cable is adjusted by the book. Report back.

[EldoRedo]

Thanks; no, this is not fuel-level related. I also added about a pint of transmission fluid yesterday as well just to be safe and so far, no recurrance. I will monitor and report back.

[EldoRedo]

OK, am reporting back as requested -- this occasional "mild" surging continues to happen. It may be happening at higher speeds, but I notice it more anywhere between 30 and 40 when I'm coasting, for example. The engine will surge up to 1700 - 1900 rpm for several seconds -- then things are back to normal. I do not believe it is transmission-related.

Any more comments would be appreciated.

[carnut]

Coasting means throttle closed, so you might be feeling the A/C compressor simply cycling on/off. 200 RPM is very slight.

[EldoRedo]

Folks,

Thanks -- I feel like I'm not describing this well enough. It's a lot more than the a/c cycling -- its feel like a "ghost foot" is briefly gently pushing down on the gas pedal. I can still hold the car in check with the brakes, but it defintely wants to pull me forward, which my a/c never has! I didn't want to make it sound too dramatic, but it sure feels somehow throttle related.

[cadillac_al]

Normally I would think this is TPS related and it still may be, but I'm wondering if maybe the when coasting, the idle is getting so low that the idle speed motor is cycling for a second. Just a thought; if it gets worse it should generate a code.

[awadecki]

Does this happen only when your foot is off the gas? If so, you'll need a new ISC motor. If not, I'd start looking at a bad ground, or misadjusted TPS.

[EldoRedo]

Thanks, OK -- here is more data: I notice this in traffic when I've just given it a little bit of gas to catch up to the car maybe 1,000 yards away -- then when I take my foot off the pedal, the engine will continue to accellerate. Coasting for me is about 1250 RPM (idle is 625). When this happens the tach will hit, as mentioned, in the 1975 range. Again, braking holds back the car; then the revving goes away fairly quickly...no codes have been set, but I have had TPS codes in the past and in fact had the module replaced once.

[awadecki]

You either have a stuck ISC motor which is not retracting, or the throttle position sensor is misadjusted. If you rcar calms down to idle properly once fully stopped, your TPS is WAY out of adjustment. If the TPS is way out of adjustment, your car must rev up quite high when you start it. Here's a simple way to fix the TPS adjustment that works for me--provided your idle in Drive is OK:

1) Observe paramater P.0.1 at warm idle in drive. My guess is that yours is reading between -2 and -3. It should read about 1. Record this value (call it value #1).
2) Shut engine off and turn key to "On" position. Enter diagnostics and observe paramater P.0.1. Record this value (I'll call it value #2). Disconnect connector at ISC motor. Loosen the TPS torx screws. Now, rotate the TPS so that parameter P.0.1 reads (Value #2 - Value #1 + 1)--trust me, the algebra is correct. Be careful with the negative signs...

So, for instance, if value #2 = 4, Value #1 = -2, you would rotate the TPS until you saw it read (4-(-2)+1)=7, since 4-(-2)=6. I hope that wasn't too confusing. Then, retighten the TPS screws.

3) Turn key to "Off", reconnect ISC and start car.

[awadecki]

If your car idle calms down when you come to a full stop, then your TPS is way out of adjustment. If not, your ISC motor is probably stuck. Check to make sure that the "Off" indicator lights up in diagnostics when you take your foot off of the pedal. If not, you need a new ISC.

Let me know if it's the TPS, and I'll provide you with my easy way to adjust it.

[awadecki]

If your car idle calms down when you come to a full stop, then your TPS is way out of adjustment. If not, your ISC motor is probably stuck. Check to make sure that the "Off" indicator lights up in diagnostics when you take your foot off of the pedal. If not, you need a new ISC.

Let me know if it's the TPS, and I'll provide you with my easy way to adjust it.

[EldoRedo]

Thanks very much -- I will try this and report back...

[awadecki]

Sorry about repeating the same thing 3 times, I didn't think it posted the 1st time. See my first post. I got lazy after I thought it was deleted.