Clearing faults with durametric caused a surge at idle

[steved0x]

I just got a Durametric to help me with working on my car (MY 2000 986 S, 105k miles) because I had been getting a CEL that would come and go ever since I bought the car several months ago, and around 2500 miles ago. When I checked my faults I had these:

P1117
P0430
P0507
P1130
P1128
P0139

(Interestingly no CEL, it was recently on during a drive back from FL but turned itself off on the way back)

The car is driving fine, the idle is most often rock steady around 675, but sometimes it fluctuates between 600-800 every second or two.

I cleared the codes with the Durametric and when I did the engine gave a little shudder and the idle immediately went up to around 1000 (maybe as high as 1200) and then it cycled between 700 and 1000 for a moment or two, before settling down at around 700. I am guessing that was because the DME was accomodating these faults somehow and when they were cleared it changed some parameters?

After I cleared them, I took about a 30 minutes drive, and the only one that came back was P1117.

The current MAF is around 40,000 miles/5 years old best I can tell from the service records (a couple of the records have only anecdotal date/mileage and this was one of them) so I think I will try cleaning it and see if the P0507/P1130/P1128 don't come back.

For the P1117/P0139, sounds like it may be time to change that sensor? From the records I have which go back the last 60k miles, only one of the precat sensors has ever been changed.

I have been checking the threads and there is some good information there; the only thing I hadn't seen was a surge in idle when clearing the codes on a running car (is that bad? I had the car running because I was checking out some real-time data streams from the o2 sensors)

Thanks!

Steve

Edit: One other semi-random thing. The CEL light does illuminate along with all the other lights when I crank the car, and it has come on and off a few times in the last 2500 miles, but when I commanded it to come on with the durametric it did not come on. I thought that was kind of odd.

[thom4782]

When you get codes indicating problems on both banks, it's often caused by something affecting both. I'd suggest doing two things that often cause fluctuating idle. Clean the throttle body and clean the MAF. Both are simple to do and described in other threads and perhaps the Pelican Parts or Renntech DIY projects. Then clear the codes and look for two things: a steady idle and no more codes. The codes may take sometime to appear because the diagnostics take some time to reset themsleves.

[mikefocke]

My pre-cat sensors lasted about 60k miles.

A list of part numbers is here and you don't need Porsche branded part or even a Porsche specialist to swap one.

[steved0x]

Mike, I got a new oxygen sensor from Amazon of all places; they had the best price for the Bosch sensors out of the places I checked. I got the part number from off your site.

Since clearing the codes I have driven maybe 200 miles, and the only ones that came back were P1117 (came back immediately) and P0430 (came back withing about 25 miles)

I guess one is for bank 1 and one is for bank 2 so I guess they are not related. Darn it... so it sounds like that cat might be wearing out.

The value for the MAF voltage when the car was off was 1.01, and at idle it started off around 1.6 when i first cranked it up, and then settled down to 1.4 something once it got warmed up a little and the idle came down. It ultimately settled at 1.3 when my idle settled down to a smooth 625. Those are within the good ranges that I have seen on this site (between .9 and 1.1 when off and between 1.2-1.5 when idling)

I bet those other codes may have been older code; so if they don't come back then I guess I am good; if they do then I will look into throttle body cleaning and checking for leaks. The car is running good so all is good except for that darn CEL

Steve

[paulv]

Regards,

paul...

[steved0x]

To follow up to this thread, my CEL has gone off and been off for over a 1,000 miles since this thread was started. The only thing that has changed was... I have moved to FL and I am getting gas at this one store that in my opinion has really good gas. When I would visit down here and fill up my FJ with this gas I could drive probably 30-40 miles further on my tank than I could if I filled up at other places. (I can't think of the brand of gas but I will drive by tomorrow and update the thread)

I didn't change that O2 sensor, clean the MAF, or do anything else.

I am about to change the oil, filters, plugs and plug tubes, and when I have the engine compartment open I will clean the MAF, but so far everything is going really good. Idle is rock steady, good power. I hate to say it, but I am thinking it may have been the Costco gas in NC that was giving my problems. I love Costco so I hate saying that...

Steve

[thom4782]

A dirty throttle body is a classic cause of a hunting or variable idle. You might give that a cleaning too while you're in the engine compartment.

A secondary air system leak might be the cause of the on again and off again CEL. it comes on in cold temperature conditions. If you're in FL, it might not start the secondary air pump. If enough good cycles go by, the CEL might think everything is working again.

All that said, I'd start along the lines you're planning. Clean everything. Clear all the codes and see what happens. If the idle is steady, the one problem solved. If you get a CEL again with an aging related code, the replace the aging part. Then get the secondary system leak tested.

Best of luck