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Surging at Cruise

scottyboost

Member
Joined
February 16, 2003
Messages
32
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0
City, State
Jacksonville, FL
Year, Model & Trim Level
98 Limited
I have a 98 4.0 SOHC. While cruising, it surges. Sometimes it's very noticable, sometimes not at all. It does it most at ~45 mph, when RPMS are low (~1900). It is not the cruise control. It isn't so severe that RPM's bounce, but you can feel it. Idle is smooth and acceleration is smooth and strong.

TIA,
Scott
 



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Mine did the same thing. I did the MAF cleaning trick (do a search for it, there are tons of threads on it) and it worked great.

That would be a good place to start.
 






Thanks, I'll do that.

Any votes for EGR? A buddy suggested that.
 






ttt
 






ttt, nobody?
 






So have you tried cleaning the MAS yet?
 






Cleaned the MAF meter, no change.

Any other ideas?
 






Mine does that now right at 45 MPH now that I have 4.56 gears in. I never noticed it with my stock 4.10s in. I first noticed it when going down a slight grade at about 45 MPH with my cruise control set. I think the problem was when the cruise was trying to control my speed by applying the gas, the slight grade caused my speed to increase to the point that the cruise had to let off. With my low gear ratio though, it slows down pretty quickly when letting off the gas. So what was happening, was it was stuck between speeding up when giving it gas and slowning down when letting off. It kept doing this until I speed up by a few MPH and reset my cruise. If it only does it at very low RPMs and you have low gears (4.10s) then there probably isn't anything wrong. Just speed up a bit or disable the cruise.
 






Originally posted by scottyboost
Thanks, I'll do that.

Any votes for EGR? A buddy suggested that.

I dont think thats an egr problem. The egr is normally open under those conditions anyways. If it wasnt opening you wouldnt notice a power increase you would just likely fail emissions on NOx.

When you say its not the cruise control do you mean that cruise isnt on or you know somehow that the cruise system is good?
 






I've seen IAC's cause that problem also...:)
 






It does it with the cruise control on and it does with the cruise control off, so I know that isn't it.

Does the EGR have varying degrees of "open"? I disconnected the vac line to it and it seemed to stop, BUT that isn't conclusive since the surging doesn't happen consistently. I plan to take off the EGR and see if I can clean it, or possibly whatever controls the vac to the EGR. My Buick had a stuck EGR, and it was easy to clean.
 






Drove it about 20 miles last night and it was smooth as glass. Maybe the MAF cleaning did do it? ??
 






BTW, I removed the IAC and cleaned and oiled it, twice.
No more surge, and been running for 9 months.
 






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