TPS problem, playing up

[diabloam]

Just got car back from bodyshop for second time as it reacted first (after I had put turbo decal on it came through on top of wing so had to get a second one from highgate - grr)

Put it back together and got it MOT'd. Everything fine for couple of days, then when I was overtaking my mate on full boost, car just cut out, until revs/(boost dropped?) when it came alive again. So seems like run of mill overboost, had wee check of hoses, nothing obvious but I carried on using it for rest of week, meaning to look at it again at weekend. Car drives fine as long as you dont give it fully welly (seems fine up to 9/10ths of full welly). Anyway today, car started from warm this affa and wouldnt rev up, kept cutting when revs start to rise till it settled back to perfect idle each time. Had wee look about, nothing obvious, started poking and what not. Eventually looked at throttle position switch on intake, rapped torch against it and heard click and idle note changed and low and behold engine reving up freelyagain. Sorted TPS was sticking. However now car idles at 1100 or so, but runs fine otherwise. Came home annoyed but at least managed to drive home, so not too bad, lol.

Anyway to the point quick 2 Questions for everybody if anybody has an idea. Firstly is the TPS now sticking open/on and is this causing my high idle problems. Secondly could this TPS problem be related to my full boost cutting out issue, or am I still right in thinking this sounds like a problem with vacuum/boost hoses or something (I have Boost enhancer fitted also, but not set to high (think about 13psi or something i see on gauge, before opens to wastegate etc).

Sorry for long post, but wanted to get clearest info across, if anybody has any further pointers about which way I should progress with this, would really appreciate it. Took me six months to do sills and wings and then get it painted and its really frustrating not having 100% of the car back. Thanks everybody for any help, and if anybody gets similar issues with TPS, I hope my minimal, so far, investigation might help them, have cool weekend all, cheers again

 

[sulzeruk]

Sounds like the microswitch is sticking in the throttle housing. I don't know if you can get in to have a check at it under the cover. Don't know what could be causing the overboost, is the cycling valve connected round the right way?????
Alasdair

 

[robwright]

AFAIK with there turbo there are two TPS one for idle to bring the car off fuel map and one for WOT (wide open throttle), which also brings the car off map and gives it all the fuel it can. I would defo consider changing both mate. Idle speed can be adjusted by the adjusting screw. Should be around 900 RPM for a car with aircon and power steering.

 

[AndrewS]

Hi All,

Idle is controlled by the Idle Control Modulator (a function of the DME) - this actuuates a mechanical valve - namely the ISV (Idle Stabilisation Valve). Becuase the idle is controlled electronically, there is no adjustment required to set idle (as air is introduced to regulate idle after the AFM and throttle valve).

Overboost protect will get triggered if the DME senses knock. Under these circumstances it will then instruct the KLR to limit boost to 0.2 bar and the DME will retard the ignition (the combination of both is quite brutal). Vacuum leaks will generally cause loss of boost, hence you need to be looking at the source of too much boost (or not enough fuel).

The high idle problem can be triggered if the DME begins to use reference data from the 3D partial throttle map. When this happens the ISV (Idle Stabilisation Valve) closes and the revs will rise with the increase in fuel (especially once the cold start circuit deactivates and the engine warms up). An Independent Specialist can test this easily with a multimeter and determine where the specific problem source is. I do not recommend substituting or replacing any components without being 100% sure if that component is responsible. Engine Management is logical and the usual causes (of problems) are the componets that send signals to the DME.

If the TPS signal is not being seen by the DME, it will continue to use the partial load map (rather than the WOT - Wide Open Throttle) map under hard acceleration. At WOT the DME does not read the AFM voltage, at partial load it does, hence will deliver less fuel. This could cause knock at high boost and result in the overboost protect being activated.

If the TPS is OK, remove the BE. If the problem goes away, you need to adjust the BE to reduce the effect it has on the wastegate signal (from the intercooler pipe to the cycling valve). If the problem remains, hook up an analogue mechanical boost gauge to monitor the boost pressure under full acceleration and see what happens to the boost. It should hit 0.7 bar (approx) and fall away to 0.5 bar.

So, in conluding - the TPS could be the cause of both your issues but should be checked and carefully refitted before resorting to a replacement.
[]

Regards,
Andrew

 

[AndrewS]

I should also add that a non functioning ISV (or ICM module) will cause the idle revs to rise to about 1100rpm (as the idle will then be unregulated).

Regards,
Andrew

 

[944Turbo]

There is info on testing it here http://www.944online.com/techinfo/ under 15
Tony

 

[diabloam]

When i was on about bad hose, I was thinking of the one that runs to the BMe (white one, as I believe this leaking would result also in the overboost protection eventually kicking in, Couldnt get it to overboost earlier today but the car is still idling high. I know where the main TPS is, where is the second. Guess my saturday is going to consist of some further investigation and if the weather is good, applying turbo wing decal (a bit if a bitch to do). Where is the ISV, am I right to assume its beside the air flow meter, i.e it bleeds air past the closed throttle. Cheers for the suggestion all

 

[egan1]

There is only 1 TPS on a turbo. The TPS in a turbo contains an idle & WOT switch; and a potentiometer for throttle position. These are combined into a single physical unit.You may need to adjust your TPS.

Info on adjusting and testing it is on http://www.clarks-garage.com/shop-manual/fuel-06.htm

 

[robwright]

Apologies I thought there was also a TPS for WOT. I stand corrected [] The ISV is located under the inlet manifold between 3 & 4 cylinders. I belive it can be removed without the need for removing the manifold but it is not a job that I would look forward to doing if I am honest. I also believe many people have had good results from simply giving the thing a damn good cleaning.

 

[robwright]

Idle speed can be adjusted and I successfully adjusted mine this afternoon. When cold my car would idle at around 850-900 RPM but when it was warm i.e. temp gauge at the horizontal it would idle at 1100 RPM which is far too high. This would at first point to a defective ISV. In order to adjust the idle speed you must temporarily bypass the operation of the ISV. To do this you must temporarily insert a jumper wire between pins B & C of the test socket (back right hand side of the engine bay) then turn the idle adjustment screw on the throttle body to the desired RPM of around 850-900 RPM for a car with A/C. Remember to remove the jumper wire when you have finished. After I did this my car now ticks over perfectly at around 850 RPM at all temperatures. If anyone thinks this is good info I will take some piccies tomorrow and post it in the new technical section.