Greetings!
For the past few months I have been having some surging under acceleration, like merging onto the highway, etc. (07 CE manual 5 speed)
I suspect the clutch might be slipping as it is close to having around 150k miles on it but maybe it is something else.
There is no CEL or any other warning indicator lights.
The surging only happens under heavy acceleration. I have had the car in fifth gear and floored the gas pedal and the tach and speedometer climb in unison.
The surging is most noticeable in second gear and the engine/tranny is not quite up to normal temp. Could oil be burning off the clutch from the rear main seal leaking?
Can the PCV cause this? I really hope!
I also know that the tranny fluid has not been changed and has caused some notchy shifting when things are cold, but it does not explain the surging under acceleration. The clutch pick up point, or contact in the pedal feels low to me. Like close to the floor board.
A normal tune up (plugs, air filter, coolant, etc. has been done within the past 20k miles)
Thanks in advance for any help!

 

Could be the clutch disk plate is failing or clutch pressure plate is not fully engaging immediately. 2nd gear could be the gear where all factors come to play to make the clutch problem more evident.

However:

If concerned about oil the clutch, might be able to check for signs of oil on the clutch assy by viewing through the starter hole in the bell housing. In theory oil would be thrown out over the assy as the clutch rotated. Look for signs of oil under the bell housing as the engine/trans housing matting is not fluid tight.

If you have the service data, check the clutch pedal adjustments.

Watch the clutch lever/slave cylinder action as someone works the clutch pedal to make sure the clutch lever is fully retracting and or not slow to retract. The clutch hydraulics might have an accumulator which buffers line pressure and might? if problems result in too slow of slave cylinder retraction when the peddle is released.

Not sure what trans fluid temp would do, given the trans is geared. Suppose thicker fluid could put more load on the clutch equating to more slipping.

Of course watch for RPM variations in sync with surges. If the engine RPM is actually changing it should show up at the tach.

There are also ways to in theory test a clutch, the internet has lots of suggestions on this.

If it is the clutch of course it will just get worse over time.

If you have a real time scanner might connect it and watch for irregularities in the data when the slipping occurs indicting the engine load is changing and or RPM.

PCV valve change and system check is a cheap and easy but not sure this is the problem.

 

Thanks for the response Joey.
Where the engine and tranny meet it is dry. No signs of seepage around where the starter goes in either.
You have peaked my interest in the hydraulics though... In real cold weather, I could push the clutch pedal to the floor and take my foot off the pedal really quickly and the pedal would come back up but not as quick as I could take my foot off. Is that just cold weather stuff? Again, when the car warmed up, things got better.
I remember someone on here bypassed their accumulator. I guess the result was a stiffer pedal but other than that it was fine. I'm not sure I'm ready to go that far yet.
Let me know what you think. And the tach and speedo both show the surging in unison.

 

If tach and speedo are working in unison then perhaps it is the engine.

The causes can be many.

Suggest starting with the cheapest as cleaning the MAF sensor and checking for vacuum hose leaks.

If you have a real time ODB2 scanner check for throttle position in case electric throttle is moving or bad TPS and changes in A/F sensor readings (bad sensor).

Suppose bad ign coils can cause this.

A lot of surging issues don't result in a trouble code which makes them a challenge to trouble shoot.

No response from IB as yet.

 

I have cleaned the MAF and throttle body recently, the surging has not changed.
I don't have access to a real time OBD scanner.
I'll check somethings out and thanks for the reply.
I say move ahead as planned since not hearing from IB.

 

Patonium -

I have a trans doc you might find useful, if you have a U250E in that thing. It's 19MB in size, but it has some diag info in that may relate to your condition. Hard to send a 19MB file via email, but if you DropBox we could link up on that and I could share the file with you there.

 

Has happened a bad A/F sensor causes problems.

Any difference in fuel tank being full versus close to empty?

Can always try the TN site.

Concur on moving ahead as planned.

 

One of the steps I have seen in ruling out ECM versus mechanical is to pop off the trans wire harness from the top of the trans and run it. If the surging goes away then the issue is in the ECM. If the problem persists it is local to the trans assembly.

 

Thanks for the replies guys.
DIYDad- I don't have drop box but I'll PM you. Interesting about popping off wire harness, I wonder why that would cause a difference?
Joey- No difference in whether tank is full or not. Anymore info on the A/F sensor?
And, thanks for moving ahead like we talked.
Again, thanks guys for helping me out. I should get some time this weekend to really look things over. I hope...

 

What I have read is that one possible error mode is the ECM getting bollexed up and sending the wrong shift points, so you get the odd surges and hesitations. By disconnecting the tranny from the ECM those ECM controlled shift points go away and you can isolate out the mechanical from the computerized. Or something like that.