Hi all,

My car feels like its bogging down till I hit 3900rpm and then it takes off. I understand the car is supposed to pick up at the higher end of the revs, though the difference between 3700 and 3900 is immense! I know this kind of feeling from cars with variable valve timing, though in my case, it feels like its being held back till it hits 3900.

I always thought this was the 2nd gear slipping, but may as well mention it... Going up hills under load, the revs will start going up, hit a point and then drop. Then struggle to climb (depends on the load and angle of the hill). Any thoughts would really be appreciated! Thanks

Have you checked your spark plugs?

Changed the Spark Plugs, Leads, Distributor cap, Fuel Pump and Fuel filter
Cleaned Injectors, Checked ECU (circuit board and diagnostic codes), Checked my timing...
Dont know where to go from here :S

Have you cleaned the throttle body out and cleaned the MAF sensor? what condition is the air filter in?

My last post wasnt very thorough! :P
I have cleaned my TB and MAF sensor as well as my filter still being spanking new!

The V6 has a variable intake control system so there are two different paths to the combustion chamber. Low engine speed it takes the longer route and at higher RPM the shorter route so possibly explains the marked difference when the revs get up there. The servo that directs the path is controlled by the ECU and the control valve is fully open by 5000 rpm not sure when it starts to open but may be around the revs you talk about.
there is not too much documentation on it.
If its auto does it behave differently when you manually select gears? Vee

The V6 has a variable intake control system so there are two different paths to the combustion chamber. Low engine speed it takes the longer route and at higher RPM the shorter route so possibly explains the marked difference when the revs get up there. The servo that directs the path is controlled by the ECU and the control valve is fully open by 5000 rpm not sure when it starts to open but may be around the revs you talk about.
there is not too much documentation on it.
If its auto does it behave differently when you manually select gears? Vee

This is a good point to look into. I think there is a valve that controls which intake the air is forced to take dependent on RPM. Dare i say an old 6g72 will have a rather filthy inlet manifold and a decent amount of carb cleaner may free up the valve.

I know of the idle speed control valve and the fast idle air valve... Is it one of these you speak of?
I have cleaned the ISC valve before. Though at the end of it all, the top end is the part Im actually satisfied with, so I would think it wouldnt come into play with this problem. Though I would love my car to work as well as it possibly can in all aspects (taking $$$ into account somewhat).

The car performs the same manually shifting gears as letting it run in auto...

Hard to remember as been a while since i overhauled a 6G72 but think the valve is on the other end of the intake manifold and a black plastic housing with a loom connecting to it. Vee

Its on the right side of the engine... I found it in the manual. Its called the Variable induction control servo. When I took it off, it snapped back against the spring loading. So I fully loaded it back up and put the housing back on. I think the wheel opens and closes a butterfly valve, though it seems to be sealed in the manifold.

Theres an electric motor that runs it. Vee

Theres an electric motor that runs it. Vee

I noticed! And the plastic wheel that connects to the valve runs up and down that thread so much, there is a groove in it. I wonder if it still does its job properly...

Have you checked the ignition timing? It should be set at 5 BTDC. There's a brown ignition timing terminal (light brown round plug) that has to be grounded - it directs ecu not to vary the ignition timing so you can set it with ignition timing light. After you disconnect the terminal typical advance is about 15-20 deg. at idle

Have you checked the ignition timing? It should be set at 5 BTDC. There's a brown ignition timing terminal (light brown round plug) that has to be grounded - it directs ecu not to vary the ignition timing so you can set it with ignition timing light. After you disconnect the terminal typical advance is about 15-20 deg. at idle

One of the first things I did... I try and try without getting any real change. Quite frustrating really! I noticed sometimes when Im driving the revs will just drop out of no where and then come back up. For a car with only 150000 and I know the first 100 was my grandfathers ks, Im pretty disappointed. Thanks for all the replies guys, but I think this is just going to remain a mystery for now!