Steve_Carragher

I have a 99 996 with a Tiptronic and when cruising steady around 1600-2200 RPM the car hesitates and I can watch the tach vary between 50-200 RPM, it is very annoying. The Porsche dealer verified the problem when driving uphill, but it did not appear to exist when going downhill. They suggested I buy 2 front tires to match the Michelins I have in the rear. I put new tires on, but it did not help. Next they want to change the fluid and inspect the transmission for problems. Has anyone else experienced this problem because our local dealer admits they have never heard or seen of this problem before but feel the torque converter may be to blame? Their only option is to replace the entire transmission if the inspection looks good visually. Does anyone have another suggestion?

redduck996

what the heck does the tires have to do with the engine hesitating?
I get the opposite, a slight boost but I think they said its the variocams kicking in or something..

Steve_Carragher

The local Porsche dealer stated that the different diameter tires "may" be the problem, they said that the Porsches have speed sensors for each wheel and that they may detect a problem and cause the hesitation. I doubted it, but took their suggestion anyway because they are the "experts". Have you or anyone you know of ever heard of my problem before?

spenny_b

Finally, last night, I overcame my hesitation problem, however, it's not as low-dwon the rev range as yours, mine happened under full load at about 2500 thro' to 5000'ish. It manifested itself as jerky acceleration, almost like I would describe a VTEC or harsh VarioCam kicking-in would feel like if you didn't know better. Of course, it wasn't pulling as hard as it should either. Idle also felt "weird", in that if you come up to a junction, dip the clutch, revs would soar up to 1400 for about 5/6 secs, then eventually drop back to a normal idle of 800rpm.

My usual Indy specialist ran PSTII diags on the car and came to the conclusion it was down to the two Lamda sensors (mine is a '98 C2 Manual)...which sounded plausible, as my Subaru's Lamda went at similar age....they all do. £430 lighter, and the prob is still there!!

Spoke to another dealer who suggested it's *probably* the Mass Air Flow (MAF) sensor, as this item doesn't log an error code, instead the Lamda tries to compensate (over compensate), runs out of range, then trips an error code to be logged.

Replaced it last night myself (friend works for Bosch, got me one for £89, versus Indy Specialist who wanted £395+Tax, plus 0.5hr fitting!!!)...Hey Presto, prob gone and I've got my old Porsche back again, and it feels SOOOOO much different!

MAF is by far the easiest and cheapes item to try replacing, all you need is a security torx bit (one with a dimple hole in middle of star) to remove the 2 screws holding it in, gentle pull to break rubber O-ring seal, and it's out. You can't see anything (hot film type, not an element), but somebody on here suggested it can be cleaned and replaced.

Hope this helps,

Spen

TT Gasman

Might be bad gas (petrol), try a can of Techcron or other fuel additive. This just happened to my Expedition, ran like crap, surging and hesitating aftera recent fill up. Took it to the dealer, fuel analysis showed contamination with Karosene?? WTF

mitch236

The tire diameter might make a difference if you have PSM but if you don't then it will have no effect. I also don't think you have vario-cam in your year so that wouldn't be a problem although even with it, the rough spot is around 3200 RPM.

First try to figure out whether the problem is in the engine or the tranny. Is the car sputtering on slipping? That would help differntiate the source

Steve_Carragher

I only use Chevron Supreme with Techron, always have but have added two different brands of fuel injector cleaner since the problem occured a few months ago, but will try a bottle of Techron. Thank you for the suggestion. I do not have PSM in my car so unfortunatly that can't be the problem. For some reason the dealer thinks it is in the transmission, specifically the torqe converter because the problem occurs when under a slight load. They have never heard of this problem before so I'm not convinced of thier evaluation and they want $400 just to change and inspect the fluid. There are no adjustmens in the Tiptronic transmission, nor can not replace the torque coverter by itself so my car would need a transmission replacement for approximatly $10,000. This is the reason I am hoping someone can suggest another problem area.
Thank you,
Steve

1999Porsche911

The first thing to do is find someone else to work on your car. Tires??? They must be morons. There are alot of possablities. You might look at the temp sending unit. A bad unit will cause a similar symptom. If there is no hestitaion at that speed on a COLD engine, that would indicate this sensor. It is located on the right side, bottom of the engine in the back below the AC pump. Remove the 4 wire connector, clean and reinstall. Variocam is not in play at that engine speed. Check all vacuum lines. What is your vacuum gauhe showing at idle. Is it steady and higher when hestitaion occurs? ? Hook up your scanner and take a close look at the O2 sensor reading while duplicating the hesitation. Also look at the long term fuel trim readings. What is the MAF reading at idle?

Does the hesitation occur in all gears? Can you duplicate it in park?

Before anything, I would disconnect the battery for a few minutes to eliminate any bad errors stuck in the computer. Much like rebooting you home computer.

wyo996

I had the same hesitation and it was the MAF. Perfect smooth acceleration now. You could also try to clean the element with electrical cleaner for a cheap fix try. Just spray it on and let it air dry. Easy to remove. Will

Steve_Carragher

I have a 3.4L and the temp runs around 220F when driving in town at 110F. The problem does not occur in park but does occur in all gears at that 1600-2200 RPM if the engine is cold or hot. It appears when just cruising not under heavy acceleration. Was your hesitation at that RPM range too? Can you tell me how to locate and clean the MAF? I would hope the dealer would have checked that first, but they only suggested transmission problems. It would be a cheaper fix that is for sure.
Thank you,
Steve

Steve_Carragher

I have disconnected the battery for approximatly an hour but it didn't correct the problem. Is there a way I can check the O2 sensor or MAF without a PSII system, the dealer did not impress me with their first suggestion? Will I damage the O-Ring if I remove and replace the MAF unit for cleaning?

1999Porsche911

Just remove the 2 screws and pull out. I wet the o ring with spit when I put it back.

Steve_Carragher

Can you recommend a good cleaner for the MAF?

1999Porsche911

The idea is to remove any oil, carbon or other grime from the sensor's surface. I use carb cleaner (really spray the hell out of it) and then follow it with a splash of rubbing alcohol. Electronic spray cleaner works well also. You can get a can at a Radio Shack.

Steve_Carragher

Thank you for the suggestions, I'll try it on Friday.