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RPM surge every few minutes - sensor? computer issue?

4K views 4 replies 5 participants last post by  Dr.[H]ouse 
#1 ·
Hey, I have a '98 Caravan with the 3.0, 197K miles on it.

I've been noticing that at 45mph or higher, when driving a steady speed on a flat road (there's no hills around here), the RPM's of the engine surge every few minutes.

Happens regularly every two to three minutes --- the van doesn't seem to slip out of gear -- speed is maintained -- but it feels like maybe a 500rpm uptick is happening. It only stays high for a few seconds, and then it goes back to normal performance.

Doesn't matter whether I have the car in 3rd gear or in overdrive.

I'm guessing this is going to be either a sensor issue -- or something a tune-up can correct.

All fluids are fine (oil leaks about a quart a week; some ticking from the engine is typical but its not too loud; trans fluid is good.)

Check Engine light has been on ever since I got the van. I know a mechanic one state away who will check it for free, so, when I am out that way next month I might have him look up the codes. Right now I'm just trying to get some ideas for what it might be.

Like I said, I'm reasonably certain this isn't a trans issue -- I had transmissions go out in some 4.6 V8 Ford's I owned... and this doesn't sound or feel like that did.

Thanks for any ideas.
 
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#2 ·
I'm sure it's the floor mats. Or EMI from solar rays. :eek:

Seriously, try disconnecting the cruise control servo, and see if the problem goes away. The cruise could be intermittently pulling on the throttle cable, even if you don't have it engaged (electronics, you know).
 
#3 ·
You can get the codes read at any parts store for free.

It could even be a bad EGR valve as my engine had a slight surge to it when the valve was going bad. Now it has totally failed and the surge has gone away.
 
#4 ·
I had some problems on my 2000. turned out to be the throttle was sticky. Lubed the throttle cable and the problem went away. I think what was happening was the cruise was trying to open the throttle and and because it was sticky, ended up over compensating and the T/C clutch disengaged due to the resulting throttle position. Just wasn't enough throttle to cause it ti kick down into 3rd gear.
 
#5 ·
Hey, I have a '98 Caravan with the 3.0, 197K miles on it.

I've been noticing that at 45mph or higher, when driving a steady speed on a flat road (there's no hills around here), the RPM's of the engine surge every few minutes.

Happens regularly every two to three minutes --- the van doesn't seem to slip out of gear -- speed is maintained -- but it feels like maybe a 500rpm uptick is happening. It only stays high for a few seconds, and then it goes back to normal performance.

Doesn't matter whether I have the car in 3rd gear or in overdrive.

I'm guessing this is going to be either a sensor issue -- or something a tune-up can correct.

All fluids are fine (oil leaks about a quart a week; some ticking from the engine is typical but its not too loud; trans fluid is good.)

Check Engine light has been on ever since I got the van. I know a mechanic one state away who will check it for free, so, when I am out that way next month I might have him look up the codes. Right now I'm just trying to get some ideas for what it might be.

Like I said, I'm reasonably certain this isn't a trans issue -- I had transmissions go out in some 4.6 V8 Ford's I owned... and this doesn't sound or feel like that did.

Thanks for any ideas.
I have a 4th gen and I have a fluxuating rpm around 25 to 40mph.
No idea what causes it still.
Hoping someone else has similar issues
 
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