chet

I've been having a problem recently with very noticeable hesitation when starting from a stopped position before the car has completely warmed up. The car is a 95 (pre-varioram) tiptronic with 102,000 miles.

I had previously almost sort of experienced this in winter and only vary rarely, and not nearly this amount of hesitation. So I'm assuming something new has happened recently.

Since I recently removed a large part of the air intake system to replace a faulty oil pressure sensor, it is quite likely that I am the culprit.

Since the problem began, I have used MAF cleaner on the MAF, I cleaned the ISV, and I have visually inspected the vacuum tubes looking for a vacuum leak.

I decided to go ahead and pull out the SAI system (on my OBDI car), and when I started pulling out the intake manifold today, I have oil actually dripping from inside. Not just an oily film (which I did have when I took out the manifold to get to the oil pressure sensor), but drops.

Does that add any information which might help diagnose my hesitation problem?

Are there tools available to the home DIYer to check for vacuum leaks?

PS I'm also replacing the fuel filter and oxygen sensor since neither were terribly expensive and I don't know whether either has ever been replaced before. (I don't have any records from prior to my purchase at 66,000 miles).

Any suggestions that you guys might have would be greatly appreciated.

Stealth 993

Sounds like a vacuum leak. Make sure you didn't disconnect any lines when you did your repair, maybe do some vacuum test.

chet

Thanks,
I was thinking vacuum leak too, I just can't seem to find it.

ble2011

I had a vintage Mercedes which are known for all their vacuum lines. I was very hard to visually locate a vacuum leak. Even when the lines looked good, they become brittle and did not seal correctly. I replaced all the lines and that corrected it. For all the lines touched, I would replace with new. It's cheap and then you can put the vacuum line issues to rest.

vincer77

Since it is related to temperature, does that maybe narrow down the choices? Of which vacuum lines that is.

NC TRACKRAT

Not a very safe way to check for a vacuum leak but "old school"...With the engine at idle, squirt a little starting fluid near any suspected hose or fitting and listen for an increase in revs. As for the oil in the intake manifold, any possibility that you've added too much oil?

chet

Thanks for the contributions guys. As far as the oil goes, it looks like the last time I added oil was a couple of weeks before I took things apart the first time to get to my oil pressure sensor. I probably would have seen the same thing then if it was already overfilled, although it was just a couple of hundred miles during that two weeks.

Does it seem like the temperature sensitivity of the problem might indicate some component other than vacuum?

vincer77

Looks like Streather describes a vacuum leak-check procedure on page 454 of the 993 book.

chet

A little follow-up on my vacuum problem.

When doing my oil pressure sensor work, I inadvertently knocked some of the hard plastic vacuum tubes out. After getting some help from this board on what goes where, I still managed to get it wrong.

I had the line that comes over to the center from the vacuum reservoir 4-way connector directly attached to the central piece of the intake distributor, and I had the line that comes over to the center from the fuel rail connected into the 4-way that uses a one-way valve to connect into the intake distributor. Those two lines should have been reversed.

I don't know for sure why that caused the hesitation, but it did mean that as soon as the engine was shut off and no longer pulling a vacuum, the section of the vacuum system that included the reservoir was open to the intake distributor without going through the one-way valve and thus lost vacuum immediately. (It also meant that the resonance flap and SAI pump vacuum lines weren't connected to the reservoir.)

Stealth 993

You didn't have your FPR (fuel pressure regulator) working, it increases fuel pressure to the injectors as you get on it. Very important!! You may have been running very rich with it disconnected.

dp2boy

Thanks for posting Chet, I have almost the exact same car ('95, Tip, Cab etc...) and have almost exactly the same problem. My problem started after getting the car back from a local shop that changed the plugs. It appears as though all the vacuum lines are on but I'll now go check to make sure they are attached to the right places.