Mike12086

been searching for awhile on how to fix this. so far have tried plugs (needed), coil, iac, & map. no engine light is on. i believe it is the pcm. if i disconnect the iac, tps, or o2 it does not pop up an engine light, if i disconnect the map it does throw a code. it does change how it runs (usually for the worst) so it seems like it does read the sensors but i thought if i disconnet one it should pop up a light? i plan to try the pcm screw thing to see if that helps but right now i'm waiting out the rain to go do any more work on her. any help or other things to try would be great.

btw its a 97 4.0 with 122k.

thanks
mike

ol"blue

I'd disconnect the battery and remove the connector from the PCM and see if there is any corrosion or loose pins there. You should get a light or code when disconnecting those items I believe.

drakan1908

I know it will throw a code when the O2 is disconnected because I accidently knocked the wire off one of mine ( back one).

Mike12086

tried the screw thing today and also cleaned the pcm connectors and nothing changed.

myhobbes25

same here

Noah

My XJ had a low/rough idle, I installed a new fuel filter and that fixed it all. Maybe that would fix your GC?

Just a thought.

Mike12086

just did some fuel pressure / vaccum testing today.
vaccum stays pretty stedy (bouncing maybe a hair while at idle). Fuel pressure on the other hand is all over the place. at idle it bounces between 46-52 (moves so much you can get dizzy watching the needle). if i give it a little gas its gets perfectly stedy at about 48. so what if anything did i find out?

Mike12086

bring back this thread since i had some more time to work on it. Replaced manifold gasket due to idle change when sparying starter fluid around everything. Just replaced whole pump assembly (pump/filters/regulator) and started up and still had presssure bouncing around at idle. Did the neon injector upgrade and had stedy pressure at idle but still rough idle and that only lasted for a couple key cycles and the bouncing pressure at idle came back (does not seem to be bouncing around as much as before). And just did wires just because.

I am really thinking computer but am still not sure on replacing it yet.

Any thing else i should check?

Thanks

Mike12086

Took a quick video of the jeep today...take a look and tell me what you think...idle does drop off more once warmed up (around 500 rpm, load usually doesnt matter).

Mike12086

just changed the upstream o2 sensor, did a reset and drove around enough for it to relearn and no change. will the downstream effect it at all? should i bother changing it? open to all other suggestions otherwise i might just give in and bring it somewhere.
To recap have replaced IAC, TPS, MAP, Fuel pump assembly (filters,regulator), plugs, wires, coil, Upgraded to neon injectors, intake manifold gasket, and upstream o2. it idles rough from a cold start but gets low (500 rpms or so) after warmed up, load does not matter.

Bustedback

You have a miss, do a compression check and see if one cylinder reads low. You may have a burnt valve.

tiwvr1

or a bad cps. Most commen thing to go bad, didn't mention replacing it yet

Mike12086

everything i read about a bad cps also says that it stalls..i have not had it stall at all. i thought about changing it just for ****s and giggles but heard it can be a pita to do.

Mike12086

bump...anything else to look at for the weekend?

greasemonky

im having that same problem with my xj