It is nice to see a discussion of this annoyance that has plagued my driving experience since buying my SHO in Nov 2000.
The symptoms are:
In D you notice that the car is 'sailing' or driving itself when you are cruising along - you can release the gas pedal and the car drives itself - the fuel is not cut-off (unlike most vehicles). If the cruise system is on, it cannot hold the vehicle speed to the setpoint very well (especially if you go to a downhill stretch of road), the speed increases.
When you come to a stop in D with foot on the brake pedal, you notice that the idle speed is around 900-1200rpm. You can feel the engine 'fighting' against the brakes and transmission load.
While stopped, if you then select N or P (i.e. take of the loading of the transmission from the engine), the engine speed will hesitate a bit and then rise in a controlled manner (sometimes at a very slow rate) towards about 3000rpm. It does not hit the rev-limiter, which is about 3500-4000rpm in N or P.
Naturally if you put it into D from this 3000rpm condition the transmission takes a huge shock and your wheels spin - not good for durability or safety!.
When the conditions exist, you will notice that the idle control (engine speed) in N or P with vehicle stopped is extremely sensitive to any additional loads applied to the engine. This is especially so when the air conditioning compressor clutches in and out - it causes a big disturbance to engine speed.
I work in the motor industry defining software and performing calibrations on many engine/transmission/traction control system functions, so have a good background in troubleshooting problems and finding route causes - including powertain electrical troubleshooting for Jaguar, BMW and Rover on their development vehicles from first prototypes to production build.
However, in this case I didn't have the necessary calibration tools or system specifications (for the idle control function and its diagnosis for example) to communicate with the engine management system directly, so I had to rely on experience and other less 'intelligent tools' to diagnose the problem.
The occurrences are intermittent - at first i thought it may have been temperature related (bad idle calibration at low temperatures), but it has since exhibited it from close to 0 degrees F coolant/air temperature to fully warm. Vacuum leaks were also suspected, but cruise etc. seems to function fine, and brake servo assist is OK when the problem exhibited.
The other thing it could be is a sticking PCV valve, which could stick letting unmetered air into the intake manifold - but I think it unlikely due to the ramping effect i have seen.
One big item that puzzled me was the way that the idle speed ramps up in a controlled manner to 3000rpm - normally if you have a direct fault (or intermittent fault), the engine speed should jump erratically or directly to a new value - as a direct result of a leaking vacuum hose or broken electrical connection to a sensor/actuator. This is not the case - it is definitely being controlled to the 3000rpm by software.
I put a generic OBDII scantool onto the vehicle (the type independent dealers can by and which all vehicle manufacturers have to support) - what really surprised me was that there were no codes stored at all (not even temporary or history) - this is a big mistake for Ford as it means they are not compliant with the OBD regulations that state that a code should be raised if a fault exists which would cause emissions to raise more than a certain level - 3000rpm would certainly meet these criteria!
The next thing i wanted to test was whether the Idle Control Actuator was being commanded to an unusually high value - or if it was 'stuck' at a high value when the problem occurred. Two problems existed here - there is no feedback signal from the Idle Actuator, just the command signal - so using the OBDII scantool I could only read the commanded %. Then, typically the problem wouldn't reproduce itself when i had the tool!!
TSB's and Ford Cutomer 'Service'
At this point I searched the web, and got some TSB info from the NHSTA and carfax.com. Three TSB's seemed relevant:
1) One TSB was about a clip sticking in the throttle pedal under the drivers foot well - not the case with my vehicle (and not the same symptom)
2) One TSB was about vehicle 'sailing' in drive - the explanation was that the calibration had extra fuel added when in D and vehicle moving, with the driver not having his foot on the gas pedal - this was to avoid a drivability issue when the driver 'tipped-in' again on the gas-pedal (i.e. the fuel avoids a 'shunt' on pedal re-application).
This definitely describes the feeling i get in D - before I stop and get the high idle speed in N/P.
3) One TSB referencing Unusually high idle.
I could not find 2) on v8sho.com, but 3) is listed as TSB 00-3-5 in v8sho.com, and lists the service fix available, part numbers and OASIS numbers - great!!
I called the Ford Customer Service line this morning, seeing if I could get them to pay for this on a 'safety' issue point of view my car is over 36kmiles - stating the unintended acceleration (a term the motor industry fears like nothing else) in D, and the squealing of tires and surging forwards of the vehicle when going from 3000rpm in N to D. I failed to mention possible OBD code non-compliance. I also gave them the TSB number 00-3-5.
Ford put me on hold, called a dealer i had visited to discuss the problem with, and 'looked' into their database. I got the response that the TSB 00-3-5 didn't exist and no TSB's exist for my vehicle. I said that i could quote her OASIS numbers and the service part number for the fix - she would not accept that the TSB existed! funnily enough she almost quoted word-for-word part of the text on the TSB under 'Service Procedure' - i said 'good quote' I can read that too!
Following that I re-iterated the safety issue and mentioned that i would be calling the NHSTA who may well be interested - but to no avail, they would not budge - just the corporate reply ' Is there anything else we can help you with today ...?'
following TSB 00-3-5, I have since called a local dealer who has a XF1Z-15K607-AB in stock for $17 - I notice that it has been up-issued since AA listed in the TSB - I'll repost when I have fitted it and see if it improves things.
I'll also fit a new PCV - which Ford does for free at 60K Miles anyway.
Has anyone else had denial of TSBs from Ford or their dealer, has anyone had the same symptoms as my SHO ? Please let us all know.
I recall an earlier thread about the later cars acting this way. The '99s
(and possibly the '98s??) have virtually no engine braking when you pull your
foot off of the gas. I don't have the idle problem, but the car feels as if it
could roll forever.
Lake Orion, MI
'99 black 29K