3200 revving issues

[vulcan1208]

For the second time in 18 months and at considerable cost ( yet again ) I have had my TB repaired but am still experiencing issues. I recently fitted a contactless pedal pot which seems to be working fine and shows all of the correct values and it seemed to get rid of the CEL's but recently I started to get a surging of acceleration again even when not pressing the pedal, this culminated recently in an event where, when joining a busy dual carriageway, the car suddenly went full throttle and almost launched me into the back of a truck. I sent the TB off to have it looked at and it came back repaired but again today after fitting the TB the car went to full throttle whilst I was sitting waiting at a pedestrian crossing. Does anyone have any ideas ? I am considering fitting the modified Volvo TB as perhaps my TB has reached the and of its life but other than that the car will be broken for spares as its worth far more in bits than it would be as running, MOT'd and resprayed example

 

[Oneball]

As you seem to have ruled out TB and pedal pot I’d want to check the wiring from both the pedal to the ecu and from the ecu to the TB.

Also need to check for splits in the intake hoses

 

[Contigo]

Butterfly issue in the TB? I'd get a replacement TB personally and then get it done properly by one of the approved reworkers.

 

[vulcan1208]

Butterfly issue in the TB? I'd get a replacement TB personally and then get it done properly by one of the approved reworkers.

The last two repairs have been by two of the best names in the business :-(

 

[davy83]

Sudden increase in throttle is pretty scary. The things that can make this happen include the following possibilities.

1. Both of the pedal sensor outputs rise to a higher voltage, and both have to be exactly the same (if different you get an error and it shuts down to idle). If you lost the 0v or ground wire off the sensor it would loose power so the output would drop to zero. if you had a resistive contact 'on the ground (corroded contacts, loose wire or gnd wire broken somewhere) the output voltages might rise together, but there is little operating room for the sensor to run at lower voltages, so I suspect this is unlikely but possible. It is also possible if the pedal sensor is faulty on both outputs in the exact same way, again possible but unlikely.
2. The ECU is sending a high throttle demand to your throttle body, despite having no demand from the pedal. Can't think of a reason this would happen but could be a result of a faulty ECU I guess.
3. The wiring from the ECU to the ETM could be faulty. Its CAN bus and so there is an intelligent exchange of commands between the ECU and the ETM and so if the wiring is faulty it might cause bad communications, but you would be very unlucky for a noisy/broken wiring system to accidentally generate the correct command for an open throttle. Much more likely to throw an error and stop, but again its possible.
4. Equally the chance of the throttle body opening the flap of its own accord is a little unlikely. It could possibly be caused by faulty rotary sensors (or internal connections) giving intermittent readings to the electronics internally so the ETM internal controller does not get a good measurement of where the flap is and opens the flap thinking its in the wrong place. So problems with the repairs, replacement sensors or wiring might cause this.
5. The throttle bodies are known to have a problem with the magnets breaking up and making the flap stick. A lot of repairers don't bother taking the whole ETM apart, and just replace the rotary sensors. For two reasons, one is that stripping the whole thing is a lot of work and 2nd because you can't buy replacement magnets. I am rebuilding old throttle bodies and using magnetic assemblies from newer design Volvo ETM's to replace the magnets as the later parts have an Aluminium sheath over the magnet which helps with this problem. However the net effect of this problem is that you blip the throttle and it stays open, and nothing you do will reduce the throttle demand as its stuck open. it will throw an error pretty much straight away, but you have to shut down the ignition to stop it, and its scary.

 

[allandwf]

Do you have the safety linked out? It shouldn't be able to do that, as Davy said above.

 

[Danny]

I had the exact same issue 3 years ago (sudden increase in revs while not or hardly touching the pedal). Took very long to find what caused it, especially since I have both a new TB and TP fitted. In my car it was caused by the wiring between throttle pot and ECU. There is a connector somewhere inbetween this wiring (approx in the passenger footwell). In the past someone had tinkered with this connector: it was removed and the wiring was just put together (by applying some tape). In time, this connection must have oxidized (this signal is extremely sensitive), causing the issue. We stripped both sides, put them back together, applied soldering and finally a shrink wrap. This solved all my throttle issues and I have never had any issue again. You may want to check your wiring as well to see if the connector is still in place. If yes, strip it and thoroughly clean it.

 

[rs48635]

For the second time in 18 months and at considerable cost ( yet again ) I have had my TB repaired but am still experiencing issues. I recently fitted a contactless pedal pot which seems to be working fine and shows all of the correct values and it seemed to get rid of the CEL's but recently I started to get a surging of acceleration again even when not pressing the pedal, this culminated recently in an event where, when joining a busy dual carriageway, the car suddenly went full throttle and almost launched me into the back of a truck. I sent the TB off to have it looked at and it came back repaired but again today after fitting the TB the car went to full throttle whilst I was sitting waiting at a pedestrian crossing. Does anyone have any ideas ? I am considering fitting the modified Volvo TB as perhaps my TB has reached the and of its life but other than that the car will be broken for spares as its worth far more in bits than it would be as running, MOT'd and resprayed example

What is the contactless pedal pot? Is this still dual voltage and same electrical parameters?

 

[vulcan1208]

I had the exact same issue 3 years ago (sudden increase in revs while not or hardly touching the pedal). Took very long to find what caused it, especially since I have both a new TB and TP fitted. In my car it was caused by the wiring between throttle pot and ECU. There is a connector somewhere inbetween this wiring (approx in the passenger footwell). In the past someone had tinkered with this connector: it was removed and the wiring was just put together (by applying some tape). In time, this connection must have oxidized (this signal is extremely sensitive), causing the issue. We stripped both sides, put them back together, applied soldering and finally a shrink wrap. This solved all my throttle issues and I have never had any issue again. You may want to check your wiring as well to see if the connector is still in place. If yes, strip it and thoroughly clean it.

Now there's a thought, I started to check that last night, I had the car idling and layed in the footwell to check the wiring as I moved it it got a very brief but substantial increase in RPM but could not be certain it was not just coincidence, I will check a bit more today, thanks.

 

[vulcan1208]

What is the contactless pedal pot? Is this still dual voltage and same electrical parameters?

It is a very well built unit and has dual voltage, I have measured the outputs and it's rock solid in giving the required voltages at closed and open throttle so I'm pretty sure it's not that.

 

[vulcan1208]

As my movement of the wiring under the dash seemed illicit a slight instance of open throttle I decided to remove the connecter for the pedal pot and hardwire the connection with soldered joints and shrinkdown sleeving, after all I don't anticipate having to change the pot again. Whilst doing this work I can see it is a bit of a mess, there are two grey wires with connectors that would fit into the connector block just bent back and taped up, there is also a red wire in the connector block ( loom side ) that connects to nothing, has anyone else noticed spurious wires in this area ?

 

[Oneball]

Have a look at the pics here: https://www.sportsmaserati.com/index.php?threads/3200-throttle-pedal-sensor.27268/

 

[vulcan1208]

Thanks, that probably explains what Lancaster Maserati did to it way back in 2005 when it constantly suffered from CEL's and limp mode. After having it recovered to them they gave it back saying it was a wiring issue, I was always puzzled because I could not see that anything had been done but this wiring "modification" was probably it. Anyway all the connections are soldered, wrapped and tucked way up into the back of the dash and so far things seem ok.

 

[davy83]

What is the contactless pedal pot? Is this still dual voltage and same electrical parameters?

I make these . Its an electronic sensor but it matches the OEM spec in every respect, with dual independent outputs, but its contactless so it shouldn't wear out. I got a bit carried away with the mechanics to try and make it both tough and long lasting, its all Aluminium machined parts, with sealed stainless roller bearings, and I originally made one for my self hoping it would outlast my car (so far so good 9 years!). I also do a matching process on the two outputs to make it better than the original in terms of output matching which is a big problem on the original, and the source of a lot of the errors.

 

[rs48635]

Thanks! Will be in touch If I need one when my 3200 has an MOT. Suspect my throttle body is the elephant in the room though.