irregular acceleration - 2003 Disco
 

I have a 2003 Disco NAS 49 state model with secondary air and 83k miles. I get irregular performance when accelerating. Specifically, on kick down it will power up nicely until 3500 or so then it seems to hang a bit before kicking in to power up to 5k. It is intermittent and my gut tells me the ecu is calculating and compensating for something on the fly as I am accelerating. I have replaced the following: New MAF, completely new cooling setup, hoses, pump, thermostat (runs perfect cooling wise), new alternator, new pas pump, new viscous fan and clutch, new Magnecor 8mm wires, new valve cover and upper intake gaskets, no vacuum leaks (that I can find at least), impeccably clean IACV valve and purge valve, clean throttle position sensor, new oil separator (all breather hoses are spotless as are the inside of the valve covers), O2 sensors are old but are not throwing codes (my Lr mechanic threw it on a test book and there are absolutely no codes, stored or otherwise), I have checked and tightened all my earth grounds, the engine is smooth when idling and with all my recent fixes runs way better than it did when I bought it. Still, there have been times when it accelerates smoothly like a rocket to 5k without hesitation. It's almost like the MAF is getting intermittently fouled yet it is a new LR Bosch MAF, worked perfect for awhile and the air induction tubing is clean and airtight. I have listened to the entire engine with a mehanics stethescope and it purrs nicely all around. No weird noises anywhere or in the timing cover (I am in the vin range). I do not burn coolant or a drop of oil. When driving normally this Disco is stronger than any other I've driven, including any '04, and I have driven many.

Possibilities:

1) I do hear a slight exhaust leak ticking (subtle) Rh side at exhaust manifolds, could an exhaust leak cause the ecu to compensate during heavy acceleration?
2) My plugs were changed by LR 5k ago but I did not change the wires until now. Could the plugs have fouled with the old wires and cause this? Changing plugs on SAI models is a bit** so I have avoided it.
3) Can O2 sensors be faulty without throwing codes?
4) If the MAF wiring harness section was faulty wouldn't that throw a code?
5) Could it be a vacuum leak? How would I test for a vacuum leak that I can't really hear? All my vaccum lines are in excellent condition visually.


Any help would be appreciated, especially from someone with an SAI '03 or 04' since those years sound and behave differently from previous years.

how is the transmission fluid, is it actually at the right level? if its not completely full it will hesitate a bit.

Why are you revving it so high?

Just to blow up the engine of course. Seriously, I only do it to test for the hesitation.

I was just thinking it could be trans. I refilled it when cold while it was running after shifiting into each gear for a few seconds as per the manual. Still get the hesitation. But since I've owned it, I've heard this low level whine that seems to come from beneath the car. Happens even in neutral. The trannie sometimes lurches ever so slightly into gear, like my old Blazer did if I had the kickdown adjusted wrong, but other than that the trannie is strong. I had my LR mechanic do a trans fluid and filter change 5k ago. What else could be wrong with the trannie, I thought the one in the 03-04s was pretty much bulletproof?

All of the Rovers tran's are pretty bullit proof.
What fluid did he put in it do you know?
It takes Dexronn III.

The DII trans is electronic, so no kickdown cable to mess with.

must have a toyota gas pedal installed hahahaha

He definitely used Dextron III.

I would start with the basics, checking the fluid level, making sure the transfer case is all the way in gear and checking the fluid level in that too.

When I get back to my garage, I will do that. I just drained and filled the transfer case so it's good. No metal shavings whatsoever on the magnet. It is tricky to top up the trans when cold as by the time I pumped in the fluid for the refill it got warm. So I will check the level immediately after starting it when cold as per the manual to see if the level is right (I think it is). If the level is fine, I'll probably drain it and check for shavings. Refill, drive for a few miles drain it again and refill so there'll be mainly new Dextron III in there and see if it shifts any better.

Thanks for the advice, Spike.