Surging RPM's at speed

[LittleBeast]

So the LittleBeast has been acting up a little recently. When I am on the highway around 60-70 mph or around 2k RPM's the engine RPM's will surge (bouncy very quickly) back and forth from 2,000-2,500. It is not down shifting I don't think, pretty sure it is just the RPM's surging back and forth while at speed. No other signs of problems. ScanGauge has read Not Ready for the past 400 miles so I have no idea if there is a engine light or not.

I already replaced the FPR today, but it is still giving me problems, I am thinking of replacing the TPS next. Thoughts?

[tom4bren]

Tranny fluid mebbe???

One thing way out in left field is to get a shorter serp & bypass your AC compressor to see if that changes anything.

I was also thinking cylinder misfire ... but you said it doesn't throw a CEL.

[LittleBeast]

Really does not feel like anything mechanical, just feels like someone is pushing the gas pedal down every half second on your behalf, hence I think it is something with fuel pressure or throttle position.

[tom4bren]

Well, we already knew that the VX had taken over your wallet. Mebbe now it's also taken over your synaptic connections and the Little Beastie is just trying to take over the operation aspects as well.

Pretty soon you'll be superfluous to the entire VX process & she'll burst forth in all her glory and become the creature she was always meant to be.

If that's not the case then I ain't got a freakin clue. Sorry.

[MSHardeman]

Ryan, when was the last time you changed your fuel filter? I don't know if that would cause such a regular issue, but it's an easy thing to check/change. Maybe remove it a blow through it to make sure that it is clear and that will, at least, remove one more possible issue.

It's tough to diagnose the problem when it only happens at speed, but have you checked to see that you are getting pressure in the fuel rails?

[circmand]

But I have seen this in another vehicle caused by floor mats sliding up. Also I would look at the fuel pump

[Thatguy]

When the rpm's surge, is the speed surging too? In other words, do you feel it slow down and speed up? If your speed stays the same I'd say it's transmission/torque converter related. Torque converters are meant to stall and have a 1 to 1 ratio. If it's acting up it may slip and stall intermittently.

[LittleBeast]

My ScanGuage finally gave me a code today, it is the 0440 one for EGR problems. I have already tried removing the EGR and cleaning the pipes and EGR itself, so looks like I will install a new EGR and TPS as soon as I can. Still cheaper then buying a new car or paying someone to diagnosis and fix for me :-)

Doesn't feel like the Transmission is doing anything, and it doesn't feel like the torque converter is slipping or anything, just acts as if the throttle is opening and closing on its own a little with no change in pedal position. Just bouncing 500 RPM or so once it gets past 2k rpm (and is trying to maintain speed or speed up slightly). I tried fluctuating the gas pedal to match the type of RPM change and it does feel exactly the same as what it is doing by itself.

[PK]

Does it do it on Cruise control as well??
Might be able to eliminate one or the other.

PK

[LittleBeast]

I replaced the Throttle Position Sensor and it seems to have fixed the issue. Inside of the TPS there is a plastic wheel which has two plastic teeth and those on the old one had been worn down by the metal throttle tab on the inside of the unit. I hope it fixed it for good.

In other news I replaced the EGR Valve, but don you all think I should just let the check engine light go off by itself or should I force clear it? If I force clear it I have to wait 300-400 miles for it to send codes again, and I need to get the VX inspected. Would the light go off by itself if the EGR problem is resolved?

[LittleBeast]

Update: nope didn't fix anything. Checked the codes, now I have 440 and 405. Cleared them and we will see what comes back. Might need to do some mods to my positive battery cable.

[LittleBeast]

When the rpm's surge, is the speed surging too? In other words, do you feel it slow down and speed up? If your speed stays the same I'd say it's transmission/torque converter related. Torque converters are meant to stall and have a 1 to 1 ratio. If it's acting up it may slip and stall intermittently.

I am beginning to think more along these lines. It is very consistent, only on the highway between 60-70mph and between 2k-3k RPM. It is hard to tell if the speed changes much, doesn't feel like it changes much at all. It maybe bouncing between 3rd and overdrive? Not sure

[Triathlete]

Like Tom said...check trans fluid. If low could cause slipping.

[LittleBeast]

I will check, I was just assuming that it couldn't have gotten low after I just filled it up this past summer and it has been parked in the garage every night with no leaks. But I will check.

[ohiovx]

Sounds like the torque converter is locking & unlocking to me. Would be nice to actually drive it to see. Really hard to diagnose drivability issues over the internet.