Well I have a head scratcher. my 2000 discovery 2 has a miss,rough idle and no throttle response when cold and or raining.
When the motor warms up this problem goes away
So far I have eliminated
1 plugs coils and wires and plugs
2 no plem or intake manifold
3 no code sets
4 O2 sensors are all new

From reading threads and using my scanner it seems that the TPS is some what erratic, the sensor seem lazy at times.The other concern is the mass air flow sensor may be acting up.

Does any member have some MAF values that I could use?

Any other info would be nice too!!!

zi am a trained GM tech and this is a little of a head stumper as I do not have litature on this vehicle.
But I got a good deal on it so now I gotta drive it.

Don

 

Follow links below to download the RAVE (Rover Automated Viewing Environment) which is the factory shop, electrical, and owner manuals.

Does you coolant temp on scanner appear logical? Like ambient when you cold start, vs -40F, etc. There have been coolant sensors skewed off normal.

Some D2 have secondary air injection, which can misbehave before warm up.

MAF can be cleaned when cold with made-for-MAF spray.

 

Well the tempature sensor for both coolant and air intake are reading correct. This morning checked I the data before start up and all looked fine. Upon initiail start up and a 2 minute run time the motor wanted to stumble when I put into either foward or reverse. I was watching the line graph for the Mass ait flow sensor and the voltage jumps around quite a bit with out putting my foot on the throttle. Is this normal I would think that this sensor should be giving a constant voltage when you are not applying any throttle. Within about a 10 second time laps the voltage will jump from 9.85v (low) to 12 then 14 or 20 volts and then back down to the 9 volt range. Mean while the air volume is not changing. With foot in the throttle about 30% the MAF will go to a high reading of 27.85v

Also could expain a little more of the air injection system this vehicle uses.

My scaner is limited in what sensors it will give me the one I am lacking is the TPS voltage. It does give me the percent open of the TPS and this sensor is nice and chrisp when giving the vehicle throttle.

I will check out the web sights you suggested.

Thanks Don

 

You should never see over 12v on anything on that truck aside from ignition. The MAFS reading should be 0-5v, but that may be an issue with your scanner, and not the truck. As to that reading fluctuating, it could be normal, or a problem. It will definitively raise and drop with engine speed, so with the truck straining to maintain idle can cause that reading to be all over the place.
The secondary air injection is a pretty simple system, it's used to inject air into the exhaust, pre-cat, to aid in cat warm up when the vehicle is cold. It has a pump, 2 vacuum operated valves, and a vacuum solenoid along with the vacuum system itself. Most '00s did not have it.
The lack of throttle response rules out a few things, like the IAC, and most mechanical parts. Does it start to run better once it gets warm, or once the ECM goes into closed loop, if you can see the fueling status with your scanner?
Just off the bat, usually when these cars have similar symptoms, it is the MAFS.

 

Agree on the volts, 14.4 would be tops from the alternator. At 27 volts the ECU would be fried. If using a "meter" vs a "digital meter" perhaps you are on the wrong scale. PITA when you can't trust your test equipment.

 

Yeah, something about being a tech for this long that makes 14 equal 12.

 

12 is perfectly fine and generic. But when the alternator regulator shorts, that can jump to 17 or a little more. This is not good for radios, in particular Motorola. I learned this after the third one was swapped out in one of my service trucks.....

 

Sorry I gave some miss information the numbers I listed in the previous reply of 9.85 up to the 27.85 were g/s flow readings from the MAFS I was receiving from my scanner. THEY WERE NOT VOLTAGE. Again sorry. It seem to me this sensor (MAFS) is all over the place with readings that are very eratic, (high, low, high, low, high, low, high, low) every second the flow (g/s) is changing according to the scanner.This will happen weather your foot is OFF the throttle or while I am trying to maintain a 2000 or 2500 rpm with foot foot on the pedal. This condition happens when the motor is first fired up and goes away once the engine is up to temp. I have a graph setting on my scanner so I am able to watch instant out MAFS g/s information.

I did clean the MAFS with the CRC product made for cleaning such a sensor. This did not seem to help at all. The sensor is not the origional sensor This sensor has a production date of of09/18/2009. So it is not too old.Can not tell the manufacture.

SO to sum this problem up again starts up fine when you put it into gear it falls on its face and wants to die.Acts like a bad fuel to air ratio command.

With dealing with mostly american brand cars my experience is that the MAFS should not act this erraticly

TPS working fine, IAT is correct, o/2 sensors all are functioning,

The scanner I have is a Innova 3160b and has limited info it will let me pull out of the ECU.

SO I ordered a new MAFS coming Sat morning

 

Ok, much better on the signal... The 4.0 should be around 17-20 Kg/hr (how the factory equip displays it) once warmed up with engine loads off. Usually just slightly higher when open loop /cold start.
If my math is right, you're reading over 35 kg/hr at idle, which is way off. I'd say you're right with the new sensor, just make sure the o-ring is there and seated properly, if not you might be creating turbulence in the air stream across the sensor.

 

Well sorry it took so long to get back to the site. I installed a new MAFS rebuildt and it was a Bosch brand. I bought it from autozone; about 150 us dollars. I tried cleaning the old one first but no luck. Well it solved the problem. I also put it back on the meter and noticed that the base /gs was sightly higher about 12,80g/s instead of the old one saying 9.85g/s. also the meter read a much steadier reading, the old one wasa all over the place.