1.8 engine revs up and down

[Redwan]

got a 93 plymouth laser 1.8L engine that revs between 1400 to 2000, keeps revving up and down..anyone here had anything similar or any ideas on how to fix the issue? btw ive tried the screw , still nothing, adjusted the cable for gas still nothing, changed the thermostat still noting, took the throttle body[/B] off and carb cleaned it and put a new gasket on that and still nothing, coolant is full, can anyone help please?

 

[skrap]

Does its have an IAC on the bottom of the TB? When that goes it normally causes and idle surge.

 

[1gdsmftw]

the 1.8 instead of using a iac like on the 2.0 uses a isc idle switch control....if it is bad cleaning wont fix it...check the seals in the tb check if the isc is compressing correctly and check your tps...also you might wanna test a new ecu just to be safe

ive owned about 6 1.8s i know a thing or 2 about em

 

[DSM1G90]

Ya, quite the easy motor to fuss with ... I have one also and doing lifters on them is so easy ... almost 200k on the thing and still runs real smooth-just had to do a cam seal and lifters on the thing so far. A belt/tensioner roller job is coming up this summer.

Usually what I've experiences on oscillating idle is that timing is so way off that doing idle settings can't settle the problem..

If it's not timing by doing the same basic 5* BTDC with the terminal grounded, then there are two procedures to set idle since they don't have a BISS screw like the 2.0's since you have to set the TPS first to the butterfly when it's at a certain position, then do the idle speed setting itself.

 

[Redwan]

it may be the timing ### i changed the head gasket last weekend and before that it ran just fine, i will definetly check the timing, but never heard of timing messing with the idle, i've messed with the tps position as well but not sure what you mean set the tps to butterfly..

 

[DSM1G90]

"butterfly"-is a nickname for the throttle plate .. comes from those big carburator days of Holleys, Carters, and Rochesters.

Basically, the butterfly is set to closed position and the tang in the TPS should be just resting on the other stop that connects to the butterfly's shaft so the sensor can accurately read what position the butterfly is to tell the ECU on how much fuel to deliver. And along with this is the idle stop and speed settings that the ECU needs as well.

 

[1gdsmftw]

remember the 1.8 is a non interferance motor...so if its off timing u wont bend valves or anything but it will run like complete ass

 

[1cleanreddsm]

Well if you did a headgasket swap, could just possibly be that you forgot to hook up a vaccum line around the IM somewhere??

 

[miguelmcv]

If your idle goes up and down from 1400 to 2000 and all the times are from the same rpm, then it could be your ECU.

 

[rush2252]

Seeing as how you just did a head gasket job I would triple check all of your intake gaskets. If you have a large intake leak/vacuum leak then it will try to adjust idle to its full extent the same with an IAC motor. Once it reaches its range it will go back and forth, if the leak is too large for the IAC to control then it will continue to surge.

If you are checking for vacuum leaks using a flammable carb cleaner and spraying it around all of your mating surface of the intake manifold works great. Just spray a bit and see if it gets sucked in. You should also hear the motor idle up if you have a leak.