surging RPM

[dzillweger]

Hey Guys I have a 2000 tiptronic with 85,000 miles last week got a CEL noticed the RPM surging between 1400 and 2000 very slightly once above 2100 no surging and she ran great. Seems to only happen while going between 30 and 50 mph. Went to Autozone got the code 1117 which is oxygen sensor after CAT not heating so I replaced both Oxygen sensors after the Cats, also changed Airfilter, Cleaned Mass airflow sensor,even unhooked the mass air flow sensor and test drove still surging Rpm thinking that would solve the problem. The CEL is gone but the RPM surging is not gone. Anyone had this happen and possible solutions? Thanks Daniel

[tboyer]

Vacuum leak? I had a surging RPM when one of the rubber gaskets behind the throttle body started to leak behind the clamp. Difficult to track down (if it is a leak) search the boards for possible solutions.

[Jaxonalden]

You can find a vacuum leak with a can of carburetor spray. Spray around the intake boots and connectors with the car idling and once the idle goes up, you've found your leak.

[RandallNeighbour]

You can't rule out the MAF or the oxygen sensors... quite often, the MAF will foul out and throw a CE code for one of the O2 sensors.

At 80k, you're ripe for a new MAF.

You should also go ahead and replace the other O2 sensors right away... they aren't cheap, but they do need to be of the same age for the computer to accurately read what's coming off the engine. If you don't do this, you'll eventually get another CE light and possible more idle problems from it.

Our cars get expensive when they hit 75k miles.

[dzillweger]

Thanks for the suggestions. I will be back at it on Monday got to work all weekend. Will try the Vacume leak test with the Carb. spray and I don't think I did the Mas Sensor test drive correct. I unhooked the Mas sensor but I did not unhook the battery before I took the test drive with the Mas sensor unhooked. Should I unhook the battery before I test drive it?
Daniel

[Jaxonalden]

You said " Cleaned Mass airflow sensor,even unhooked the mass air flow sensor and test drove still surging Rpm thinking that would solve the problem." Cleaning a MAF requires a certain cleaning agent, the wrong stuff will damage the unit. I've never heard of a test drive with the MAF disconnected.

[dzillweger]

I cleaned it with Mass Air Flow sensor cleaner. I read on another Forum that if you unhook the Mass flow sensor the cars computer reverts to a factory setting and you can drive it for a short time to test drive. If the problem you are having does not occur then the Mass air flow is unhooked the problem is the Mass flow sensor. I was not clear on if you need to reset the computer after you unhook the Mass for the computer to realize it is not there and revert to the factory setting or would it sense that the sensor was not there. During the test drive I did this week with the sensor unhooked the car never threw a CEL light even thought the sensor was unhooked. Thanks for the reply!
Daniel

[caymanboxter]

Hi,
Did you get to the bottom of this? I have a 2005 Boxter that has a surge between 1400 and 2100rpm in 3rd ,4th and 5th gear under light acceleration. The surge affects the RPM by just 1-200 rpm.
thanks
Adrian

[sickbananas]

I had surging problems but not as bad as you are mentioning and no cel. I did the following that sorted out the problem.

-cleaned my air filter
-cleaned my intake and throttle body
-cleaned my maf
-reset my e-gas pedal

Not sure which step or, if it was a combo of one or two that sorted out the problem. They are all easy to do and any would recommend doing it to know that you can get to the bottom of your problem by a process of elimination. I know you have mentioned that you have cleaned your maf already.

[steved0x]

Surging at idle is often a dirty throttle body; I was plagued by that. Over time the computer would learn and adapt but the surging/hunting idle was still there. After cleaning the TB it was rock steady.

Throttle body cleaning on 2000 Boxster S