I am assuming the Kjet on your 740 has the same CIS system as 240s. I don't think the rough idle has anything to do with the Kjet, it is the constant idle system. I drove my 240 for about a year without the CIS (the computer for it did not come with the car). It idled very smooth untill I fixed the CIS. It still idles well but you can feel the CIS system making adjustments in the idle. I am thinking about hunting down an "aux air valve" for my 240 and doing away with the CIS. My old kjet Saab 900 used this and it had a very smooth idle. Just disabling the CIS does not work because the engine stalls when cold. You have to keep your foot on the gas which is trickey on a hill with a standard.

The previous posts are a great start. Leaky injector seals will always give you a hard time. Also the TPS must click when the throttle closes so the CIS (Constant Idle System) can take over and set a steady idle for the engine while you are waiting to move on. Keep in mind that the biggest enemy to the K-Jet system is an air leak. Any air that sneaks between the Air Sensor Plate and the intake valves robs the plate of the movement needed to adjust the air/fuel mixture acoordingly. Keep looking and checking everything for a possible leak. Also run a (20 oz) bottle of TECHRON on a tank of Premium to get a good flush through your fuel system. If the fuel filter has been neglected you may want to replace this after the flush. My Volvo Specialist always recommended the "TECHRON + Premium gas flush" as to the "pay $80 to flush my system type flush" and I must say that so far it has worked great for me. Good Luck!

Sincerely,
--
Julio Meza

1979 264GL B27F 122K

Features Added:

BW55 To M46, Central Locking System, 25mm IPD Front Sway Bar, 81+ Dash W/ Oil & Ambient Temp Gauges In C, Oil Pressure, Volts

Next Project:

+Cruise Control

When you have finished cleaning the throttle body make sure the throttle plate stop screw is set correctly ( A in the pic below)

Also check for correct operation of the throttle position switch (B)

Often on these systems people try to adjust the idle speed by adjusting the stop screw instead of the plastic knob (D), and this can cause problems.

Colin.

1990 740SE B200E/M47, remote C/Locking.

what about leaking injectors or holders. every kjet i ever bought, first thing, pull the intake and the cam. this closes the valves. then i spray gasket remover onto the intake valves. clean the throttle body and valves, replace the injectors, holders and seals, plugs, timing belt and seals and make sure the valves are not out of adjustment. in the 15 years i've been working on volvos, i've replaced 6 or 7 shims on the dozens or so cars i've checked. they do get out of spec, just not often. the idle will be as good as it gets, providing you are not running a k or vx cam. good luck, chuck.