i have a problem with the wifes vitara,its a 96 sport 1.6 8valve injection.
it starts ok,fast idle ok,pulls well up to the speed limit and beyond.
BUT,if you hold the throttle steady at 1900 rpm the revs drop to 1500 and back to 1900 and back to 1500.
above 1900 its fine below 1900 its fine,when in traffic in 1st or 2nd it kangaroos along and you have to change gear to get it out of the 1900 area.
ANY IDEAS???

Wild guess...

    I would have it checked for the TPS (throttle position sensor) and the O2 sensor. Hunting like that often is a symptom of an overly rich condition. Did it come up suddenly or gradually get worse?

Zag

If it was the O2 sensor, it should also be throwing a Check Engine Soon light, as a 96 is OBD II

the fault has been there since we bought the vehicle a while ago.there is no check engine light showing.

Crikies!

It's a UK '96.  Which brings up the question:  Did ALL the Tracker/Sidekick/Vitara assembly lines switch over to OBD II at the same time ('96)?

It is kinda odd that the "Check Engine Light" did not illuminate.

I can't lay my hands on the '96 GM FSM right now, but I'd check anything mechanical around the intake manifold:  

Exercise the electrical connectors to insure good contacts (except for the Injector wiring connectors! Too much trouble screwing with them).

Check the vacuum hoses for looseness- spray the joints with WD-40 or other mildly flammable solvent. Doing so will cause the engine to rev if there is a leak where you spray.  

Check any black (ground/earth) wire that bolts to the engine or body in the engine compartment for looseness or corrosion.

And look at the throttle position sensor like Zaggy says.

Good luck!

AFAIK UK models aren't OBDII. Run it till it does it for a bit, turn it off and check the plugs. If it is running rich then it could be the Water Temperature Sensor, it might be running on the 'cold' map. Air Temperature sensor will also affect fuelling as will just about everything else. The only thing you can really do is to work through all the diagnostic procedures till you hunt it down. A good place to start is to check all the vacuum pipes and earths. Could be worth pulling off the EGR too and checking thats not coked up.

thanks for the ideas,its a spanish built vehicle with the throttle body injection.not the multi point.

Does the CEL come on at all? It should come on when you first turn on the ignition.

just been and checked,yes the check engine light comes on when you turn the ignition on,and goes out and stays out when it starts.never comes on again whilst running even when the fault is occurring??

There aren't that many faults that it monitors. I just wondered if the light had been disconnected when you bought it.
Theoretically it can detect the following:
O2 Sensor (but not heater circuit)
Water Temperature Sensor
Throttle Position Sensor
Air Temperature Sensor
Vehicle Speed Sensor
Ignition fail safe (not sure that I've even got that)
Pressure Sensor
Idle switch
ECM (permanently ON = fault)
Normal (code 12)

Which leaves the EGR valve, TO, injector and a load of other circuits. You also have to consider bad grounds, the ECU can't really tell if the signal is at the wrong value. It can only look for certain conditions, ie, the idle switch turns off but the Throttle Position doesn't change and vice versa.

Wild guess...

OK, I vote for a bad MAP sensor, major input
to the ECM for fuel values.

Wild