New symptoms showed up couple days ago. Driving on the freeway, if I try to keep a constant speed, sometimes the transmission can get into a oscillating mode with engine revving up and down couple hundred RPM. It's as if trans is engaging then disengaging. Another symptoms which is more predictable is if I let off the gas, RPM drops a little, then tip in the gas, RPM will raise a little then drop (which I think is normal operation) but then a second later I feel a jolt. Other times it seems like engine RPM is too constant and I have to push on the gas a little more than expected to go faster. Does this sound like an internal transmission problem, some external (valve body, solenoid) or electrical problem?

I'm planning on flushing the tranny this weekend see if it helps. Since this is a '99 C70, do I need to use the J3309 fluid or can I get away with Merc V? The previous owner did regular maintenance including the suggested "maintenance interval" work. I've only had it 1 year but did put almost 30k miles on it so far. Fluid still looks pink and level is good.

 

Before I started the trans fluid flush, I decided to check codes. The CEL had been on due to P0030 (O2 sensor heater circuit error) so I didn't think to check code until now. Got P0236 and P0237. A search indicates turbo boost sensor problem. Other posts indicate it's one of the 2 sensors just before the throttle. Which one is the problem? Lots of online places show the MAP or altitude sensor as the one farther from the throttle (slanted shape, 3 connector, http://www.fcpgroton.com/product-exe...ategory_id/111), but I haven't been able to find anything that resembles the other sensor, which looks like a tiny MAF (little bulb with 2 connectors). Is that the boost pressure sensor? Does it go by another name?

Just for kicks I hooked up the bulb one to the meter and reading was 0V. Blowing across the bulb didn't get any readings either. Perhaps it's grounded out or I can't blow enough air across it? I cleaned both sensors with some spray electrical cleaner. Could not start the car afterwards until I disconnected the battery. Seems someone else had the same problem and they couldn't start the car until he disconnected the air filter.

Just noticed in the picture that there is a nipple at the bottom of it. Mine doesn't have that piece. Broke off?

 

Problem seems to be fixed after I replaced the MAP sensor. I didn't go for a long drive, but I cleared the code and it didn't come back. The sensor seems to go by different names like altitude sensor, barometric sensor, or boost pressure sensor, but in the end, it's a pressure sensor. FCP Groton has 3 parts listed: MAP sensor which lists for $89.99 or aftermarket altitude sensor for $95 and OEM altitude sensor for $150. I don't know the difference between the 3. In the end, I got it at CarQuest locally for $79.99 and it's the identical part as what I replaced. Same markings, same numbers. Part number is C7044302057. I hope this part # helps somebody save some money when they get a P0236 or P0237 code.

 

Info o'plenty. Thanks for the post. That may come in handy one day!

- Goat