So there are multiple problems with my 2003 S-type. I recently noted a leak of coolant, replaced what I thought was the culprit hose only to find that the leak persisted. So in the process of replacing the front brakes, I made it my mission to find the leak. I found it, bad water pump. Figured I would change the oil while the skid plate was off, and clean the throttle body. I think this is where my problems started.

I let one jack down to angle the car as to allow the flow of the carb/throttle body cleaner out of the intake. I did not remove the IAC or the TPS. I don't believe this had ever been done. I started the car up, and as anticipated it was rough at first as the remaining cleaner was being combusted. It was better, until I began driving and noted that as I would stop, there was a sense that the car wanted to idle higher. It was fighting to stay stopped at the intersections. If I were to take my foot off the brake it would actually idle to point of shifting in to the 2nd gear and get up to 15-20mph.

I researched this, I checked for vaccum leaks, then had seen that sometimes the computer needs reset. I removed the positive terminal from the battery for about 2-3min. Then started and now I have what has been termed as "the lurch". Now the car despite stopping smoothly is idling high and causing irratic shifting in the low speeds.

despite the ideas that this originates in the gearbox, I only noted this "lurch" after disconnecting the battery trying to fix the problem I started by cleaning the throttle body. I really feel that this is related to one of the sensors, either the IAC(God I hope not!!) or the TPS. I have not actually done a "hard reset" of the computer and I need to get my radio code before I do, but does anyone think that a hard reset in the format of removing the neg terminal for 45-60min will indeed work for this? I am willing to try it, but I certainly don't want to make things worse and I can't afford another gearbox.

Any other ideas? I am desperate at this point.

 

Ok, you checked for vaccume leaks and none were found? All electrical connectors snug? A "Hard re-set" is performed by disconnecting the negative battery cable and touching it to the positive terminal for 30 seconds. You must then drive her in "Normal" trans. mode for at least 100 miles or more, driving "Normally". Here, she'll re-learn appropriate shift sequences (anti-lurch). From there on drive her hard in "Sport" trans. mode. Re-check your throttle body work.

 

Frankly, leaving it disconnected for 2-3 mins is as much of a reset as you'll get (without a dealer-type OBD tool) unless you're unlucky, plus if it's behaving differently (as you clearly state it is) then you've already done a hard reset. Nothing more will occur after 45 mins or any other time or runes (whether touching + to - or whatever).

What happens is that you clear out the learned stuff stored in the PCM's memory - which is volatile. The dealer-type tool can clear non-volatile stuff in e.g. TCM. You likely do not actually want to do that.

Clearly you have a fault. Disconnecting the battery with that fault present may have made your life harder, as the car has now relearned (or tried to) but will have assumed that no fault was present as it did so. It will be trying to compensate for the fault by changing those values it normally tweaks as an the engine wears / due to manufacturing tolerances / etc.

Please stop disconnecting the battery and instead try to find the fault(s).

If you might have an air leak, hunt hard to find it.

I'd get an OBD tool and then:
1. check for codes - DO NOT CLEAR THEM - hope you have P1111
2. check the engine runs CL (closed loop)
3. if so, check the fuel trims at idle and 2500rpm

 

After months of problems, I was able to get my car into a Tech. There were so many issues that had been logged in the ECM. I had multiple issues with misfires and high idle, Air low issues. The Tech had determined that the Throttle body was the culprit for my problem after all. He tested for leaks, tested the TPS, tested the ECM. All seemed in proper order. I was forced to order a new TB. I received the one for my car, which wasnt the right TB. It was spec for my S type by all the auto parts websites, but was not the right one. After finding out that the TB was going to be >850 dollars, I decided to physically take the TB off the car to examine it. It seemed that the butterfly valve was not completely closing. I took off the TPS, examined the bore to assure there was not an obstruction, then opened the control module on the other side of the TB. Somehow the spring in the TB control module was off. I loosened the screw until the valve was in the completely closed position. I reinstalled the TB, turned on the car and NO LURCH!!!! I was overwhelmed that it worked.

I wanted to let you all know, in case others have issues with this. Apparently there was a recall on the TB for some issue similar to this. It may be as simple as adjusting this valve to assure that it closes properly.

Thanks for all your help and advice on this.

 

So I had test driven my car last night and everything is better mostly. The only problem I have now is that when the car gets on the highway to 70-72mph, it will not accelerate past this. I will peg to the floor, the engine will rev to 6000 RPM but will not increase mph. Not sure if I need to adjust the cranks in the throttle control module or reset ecu to allow to relearn after the adjustments. Between 0-70 the car shifts well and has good power, its almost as if there is a governor on the car set for 72. Any thoughts?

 

I don't think you should have touched the screw, I seem to remember that these are set, and you may have just needed to replace the spring, If I can find any more on the screw as it was posted about on the UK forum which is down at the moment

 

barney is spot-on, set the screw to its original position and all should be well.

 

I can reset the screw, but the problem is that when the screw was in the "original position" the butterfly valve was slightly open and after $200 worth of Diagnostics it was determined that the TB was the problem. Once the valve was closed the car was running much better. The only problem is the lack of acceleration past 70mph. Would this happen if the valve isn't opening all the way? I was considering readjusting back toward the original position, but it seemed counterintuitive considering the problems with high idle and downshifting to 1st gear. I can't believe all this has happened because I cleaned out the TB. amazing what happens nowadays in trying to do a little "preventative maintenance".

again thanks for your help on this.

 

Something is still up with your car, perhaps aside from the TB.

 

+1

 

Do your own diagnostics. You can do a staggering amount with a cheap elm327. Start by checking for codes then that it runs CL (closed loop), then look at fuel trims at idle & 2500rpm. Post results here

 

If your car revs to 6k and wont go over 70 mph and its in gear, the trans is slipping. The butterfly in the throttle body is not supposed to be closed all the way. It is supposed to have a slight mechanical air gap. This is why when people cllean their tb's theyll idle higher at first. The ecu has adapted to lowered idle from deposits by opening the idle air control valve more. After you clean the tb and restore the mechanical opening the iacs is still in the "adapted" position till relearned.

 

I still need to get the fuel trim at 2500, but I did remove the TB again and readjusted to allow for the slight mechanical air gap. It was trial and error to get it to where it needed to be, but it is running great now. Consistently running well on the Highway with maintained speeds >90mph then slowing to a stop without "the lurch" from 2-1 and idle at around 700-800. Working great, didn't need to replace the TB, which makes me happy. Though I still need to assure that it is running optimally from computer standpoint. Taking it back to my repair guy to have him clear the codes to see what pops up after that and will get the fuel trim data as well as closed loop. Thanks All

 

Hi m8

Sorry to but in on this thread but maybe this could be the issue I am having.

Unfortunately I did a whole lot of stuff on my car, changed all the filters, gaskets, oil, fluids, coolant, spark plugs, gaskets etc. etc.
I also sprayed lots of cleaner into the throttle body, air control valve maf sensor etc. etc.

My lower elbow in the V did have a hole in it and the 90degree elbow on the rear engine was replaced too.

My problem is that when I depress the clutch pedal I get a very slight surge/increase in revs by approx 200-250rpm if changing up gears below 3000rpm and the revs fall a little slower than one would expect. So if you change gear really fast for example 3rd-4th with rpms sub 3000rpm when you place into 4th gear the revs could be higher than actual road speed which cause a bit of lurch and not so smooth gear change. If I change gear slowish then not an issue or if I rev the car beyond 3000rpm then not an issue.

I have tried also resetting the ECU, to do this I disconnected the batter for 60 minutes, started car up, allow it to warm up, then switched off and started immediately back up and left to idle for 2 minutes. I noticed after this the engine was racing when changing gear, as high as 3000rpm, but now its calmed down a lot too as per above in the last 20-30 miles I've done.

But I'd really like to get the car spot on, so is there anything else I can try or will simply putting another 100 miles or so on the car cure this?


One thing I did not do when I changed the PCV elbow, was to change the PCV valve as did not realise it was down there too. Could the PCV valve cause the issues I am witnessing?

Apart from that all the work I've done on the car has certainly unleashed some power as the car pulls much stronger now, actually feels like I've got a full 240 horses, just wish I could stop this minor RPM surge when changing up gears at low rpms.