surging

[stevegeddes]

1999 Dodge Dakota 4x4 Sport with a 5.2L V8 SMPI OHV (gasoline)

While driving at a sustained speed (anywhere between 40 and 70 miles per hour), the truck intermittently surges (around 250 rpm’s). This may occur 2 or 3 times per minute and then not happen again for a minute or two.

On the one occasion that the truck was driven on the hiway for an extended period of time (2 ½ hours), it continually surged throughout the trip and the idle seemed to have increased at the end of the trip. In addition, the “check engine” light came on for approximately 1 day and then went off.

I took the truck to a local mechanic, who pulled the codes. It was showing a code that indicated that the problem was a fuel injector circuit malfunction. The codes were cleared and the truck ran fine (except for the intermittent surging, which it still did).

I replaced the spark plugs and wires and this did not correct the problem.

My mechanic was not convinced that the problem was not a leaking head gasket or crack in the head. A pressure test was done and it showed no visible signs of leakage. The truck has never gotten hot.

The next “test” that has been suggested to me is to see if the screen in the gas tank is slightly plugged and causing the fuel sending unit to malfunction. This would require that the fuel tank be drained and pulled.

I am at wits end trying to find the cause of this problem and do not wish to keep trying “experiments” to try and correct the problem, that really don’t work.

VERY IMPORTANT / UNUSUAL / WEIRD: I noticed that the truck only surges when the cruise control is on. It has never surged while accelerating or when the cruise control is off. So I tried a little experiment. I turned the cruise control off and drove at a constant speed (on a flat and straight road) for approximately 1 mile. Not one time did it surge. I then turned the cruise control on, and within 15 seconds, the truck surged. I repeated this procedure for about 10 miles. The truck never surged once, while the cruise control was off (again driving at a constant speed on a flat and straight road), but every time I turned the cruise control on, the surging problem returned.

[fredjacksonsan]

Did you tell the mechanic that it only does it when the cruise is on?

[stevegeddes]

Thanks for all the help and advise. I replaced the TPS last Friday and it took care of the problem. My mechanic is a little upset since he didn't get a chance to pull my gas tank and replace the screen/filter, replace the heads or replace the intake or pleum gasket. All it took was a little $25.00 part and 2 minutes of my time.

[Gizmokid2005]

It's always the little things that break!