Help! By Cars Poorly

Kazi · June 20, 2009

Hi all,

My car does not seem to be running 100% of late and on a couple of occasions the car has sort of misfired when traveling at reasonable speeds when I've needed to accelerate sharply. It sudden splutters badly as if Ive slammed the brakes on for a brief moment before accelerating back to normal.

Hoping some genius on here can tell me a little bit more about a fault that has appeared on my cars ecu. "P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction" is the exact code and description. Has anyone else had this or knows a bit more about what this entails costs wise etc.

The cars dash warnings lights (TRC Flash/Engine Light) have gone now and the car is running ok now... (until it happens again).

Many thanks in advance,

Kaz.

aztecbandit1 · June 20, 2009

Sounds like you have a black box/FCD problem matey, mine did the same when i didnt wire in the fcd properly when i fitted the charger? but not sure what you'll need to do? Have you got the FCD or the Black box on yours?

Kazi · June 20, 2009

Black standard box. Found some better search results on google as I had little joy on here. Sam had an issue like this and he replaced the vac sensor. You about Sam? Part number how much is this part? Oh and is it easy to fit? Cheers all.

Oh, what happened to your IS dude? Just noticed your signature....

Steviewevie · June 20, 2009

Could there be a wiring problem, e.g. something has come loose in the wiring of the black box/ECU ? Are they proper soldered connections or is it scotchlocked ?

Steviewevie · June 20, 2009

Black standard box. Found some better search results on google as I had little joy on here. Sam had an issue like this and he replaced the vac sensor. You about Sam? Part number how much is this part?

The vacuum sensor is 89421-20190 and is around £200, so you're going to want to be pretty sure this really is at fault before swapping it !

Kazi · June 20, 2009

Ouich...£200...

The piggy back is soldered, I will have a close look tomoz to make sure the solder is still good and the ECU is secure. I was guessing at it being the vac sensor as Sam said that seemed to cure his....if im honest i have no idea what it is... :duh: :shutit:

Kazi · June 20, 2009

Do you think it may be a good idea to remove the pre-cats from the manifold?

Steviewevie · June 20, 2009

Do you think it may be a good idea to remove the pre-cats from the manifold?

Someone may correct me, but I don't see how that could be connected since the vacuum sensor is measuring the pressure before the air goes into the engine, and your pre-cats are after the engine. Sorry if I'm misunderstanding you though and you're asking an unconnected question.

Kazi · June 20, 2009

Do you think it may be a good idea to remove the pre-cats from the manifold?

Someone may correct me, but I don't see how that could be connected since the vacuum sensor is measuring the pressure before the air goes into the engine, and your pre-cats are after the engine. Sorry if I'm misunderstanding you though and you're asking an unconnected question.

lol, yeah sorry, it was a little random. Im just googling and it seems that removing the pre cats is a good idea in general for forced induction cars. Im a little concerned now after reading about it that they can often break up and cause issues with the engine.

Back to the PO105 Is it possible to just clean the vac sensor?

If I replace the Piggy back ECU with another one I have spare somewhere, and then erase the error code from the ECU, will it come straight back on if its not sorted it?

Steviewevie · June 20, 2009

lol, yeah sorry, it was a little random. Im just googling and it seems that removing the pre cats is a good idea in general for forced induction cars. Im a little concerned now after reading about it that they can often break up and cause issues with the engine.

I do remember reading about that, yes, but hasn't that only been on cars where the charger has been pushed a fair bit above the stock TTE setup ?

Back to the PO105 Is it possible to just clean the vac sensor?
If I replace the Piggy back ECU with another one I have spare somewhere, and then erase the error code from the ECU, will it come straight back on if its not sorted it?

I don't know if you can clean it, but I can't see it hurting to try. At least you can see whether there's something obvious blocking it up.

The manual talks about needing a couple of trips to work out if an error is a real one or not but this doesn't square with what I've seen, which is that the error can come up straight away again. So I'm not completely sure, but I think it's quite likely to come back up again immediately if there's still a problem.

Kazi · June 20, 2009

Im not sure how others have come to the conclusion its the vacuum sensor. The OBDII just tells me the code. Not exactly specific really. Some say its the Piggy back going faulty.

I don't really know where to go from here without having to take it to Lexus and them pull my p*nts down parts/labour etc.

The car has spluttered, misfired a few times before and no warning lights have come on until the other day, why is that?

Gord · June 20, 2009

Im not sure how others have come to the conclusion its the vacuum sensor. The OBDII just tells me the code. Not exactly specific really. Some say its the Piggy back going faulty.
I don't really know where to go from here without having to take it to Lexus and them pull my p*nts down parts/labour etc.

The car has spluttered, misfired a few times before and no warning lights have come on until the other day, why is that?

To make sure on what the problem could be, take your black box off for a few days, re-set the ecu, and see if you are still having problems mate.

Kazi · June 20, 2009

Im not sure how others have come to the conclusion its the vacuum sensor. The OBDII just tells me the code. Not exactly specific really. Some say its the Piggy back going faulty.
I don't really know where to go from here without having to take it to Lexus and them pull my p*nts down parts/labour etc.

The car has spluttered, misfired a few times before and no warning lights have come on until the other day, why is that?

To make sure on what the problem could be, take your black box off for a few days, re-set the ecu, and see if you are still having problems mate.

Thing is though, it only does it when I suddenly nail the pedal down, even then it only does it once in a while. I think I have a spare black ecu some where as I know in the past I had an issue with the car turning off as soon as I touched the acc pedal.Once replaced it was fine, until now.

I can see the Vac Sensor, doesnt look to hard to get at and clean. Gotta be worth a go to.

Thanks for the idea Gord, don't have a huge amount of confidence in touching the ECU and removing the piggy back box. Im gonna need to take the charger belt off aswell aren't i?! D'oh!

Is there anyway of testing the Vac Sensor?

Steviewevie · June 20, 2009

P0105 is connected with the vacuum sensor according to the technical manual. You can read the troubleshooting procedure here. The procedure to test the vacuum sensor is here.

Bear in mind though, that your car is supercharged, so you're forcing more air in to the air intake (and therefore past the vacuum sensor I presume) than normal, and the manual doesn't cater for that. The TTE black box is there, I understand it, to stop the engine cutting the revs because it thinks there's a problem, so it has to fool the ECU somewhat.

Given that the TTE black box is unreliable, and the similarity of your symptoms to others with a dodgy black box, I think it's highly likely that's where the problem is. But it's still worth cleaning the vacuum sensor, yes, since that should be pretty easy.

You won't get a warning light for every single little problem the car has, the ECU will decide if it's serious enough to put the light on. So your car may have had small issues before but now it's got worse.

Kazi · June 20, 2009

P0105 is connected with the vacuum sensor according to the technical manual. You can read the troubleshooting procedure here. The procedure to test the vacuum sensor is here.
Bear in mind though, that your car is supercharged, so you're forcing more air in to the air intake (and therefore past the vacuum sensor I presume) than normal, and the manual doesn't cater for that. The TTE black box is there, I understand it, to stop the engine cutting the revs because it thinks there's a problem, so it has to fool the ECU somewhat.

Given that the TTE black box is unreliable, and the similarity of your symptoms to others with a dodgy black box, I think it's highly likely that's where the problem is. But it's still worth cleaning the vacuum sensor, yes, since that should be pretty easy.

You won't get a warning light for every single little problem the car has, the ECU will decide if it's serious enough to put the light on. So your car may have had small issues before but now it's got worse.

Thank you very much. Thats put my mind to rest a little. If I can just find my black box...

Will update topic for others.

Many thanks.

sparkystav · June 20, 2009

I will almost gaurentee its the black box mate

Kazi · June 20, 2009

Cool, cheers guys. Just thrown me a little as other replaced the vacuum sensor. I have a spare black box so will get it changed. Im also wainting to hear back from TTE as im hoping they will send me another one as replacement spare.

Cheers again...

Kazi · June 27, 2009

To close the topic off. *UPDATE*

After contacting TTE they agreed that it was most likely the Black Piggy back ecu thats failed. Unfortunately, these are no longer free. They quoted me €299. Lucky for me, I found a brand new I had which Florian sent me after my previous one went bang.

Installed this and ran the ODBII scanner and no DTC codes are shown. Car is now running tip top again!

Cheers guys.

Steviewevie · June 27, 2009

Great news, well done ! :D

TTE now do a Silver Box, which is supposed to be slightly better than the old Black Box.

Kazi · June 27, 2009

Great news, well done ! :D
TTE now do a Silver Box, which is supposed to be slightly better than the old Black Box.

Im awaiting a reply from them again. I explained to them that the last one I had was free so I was somewhat shocked by the price they are asking for. Will see what they say. I will ask them how much the Silver one is. Whats the difference? Does it let the revs go higher? 200rpm extra?

Steviewevie · June 27, 2009

Stav did a great write-up of the various ECU options here, and it mentions the Silver Box there. He says it takes an extra feed which helps it work better, and actually slightly reduces the rev limit (for good reason).