2.8L TBI Rough Idle

[Joiner]

My 2.8L has about 118K miles on it, 5speed manual T5, gets me 29 mpg to work driving an average of 55mph, but often it has a rough idle. This truck has been through two deer, dont think that's a cause though. The fan guard sits loose but doesn't hit the fan and nothing but the bumper, grill, and headlights were damaged other than that. I did read somewhere that this might be the intake or TBI gasket, but wouldn't I then be getting crap gas mileage?

[Tink]

Rough idle is often caused by vacuum leaks (could be vacuum lines or bad gaskets)... I take it you are not getting a check engine light?

[Joiner]

No check engine light, could this be caused by exhaust leaks before the cat? Lack of appropriate back pressure? What is my idle supposed to be at for a manual? It's going at 800 RPMs.

[neo71665]

Vac leaks or the IAC needs to be adjusted

[Tink]

Is that 800 in neutral or in gear?

[Joiner]

That's 800 with clutch disengaged. If I let it get below 1000 while in gear it gets doggy.

[Tink]

Should be about 950 in neutral... of course, mine is carbed, but I wouldn't think it would be much different.

[neo71665]

My auto 2.8 idles about 850 with a bad tps. If it gets below that it starts missing bad and you have to goose it.

Yes give me crap fror having a bad TPS. I have another TB I'm rebuilding and putting all new sensors in so I just been driving it as is.

[Joiner]

Some days it idles fine at 800, no hiccups, others it just shakes a little, it's not real bad or a miss or anything but it is noticeable. I had thought it was because the heat riser off the exhaust manifold to the intake was gone but now that winter is over and it's still having the rough idle I decided to look into it. This Saturday I don't work and I'll be under the hood changing oil and looking around. A day or two ago the thing wouldn't start for me, it'd act like it was going to but just died after a few seconds, wouldnt get above 600rpms. After three or four tries it started.

[neo71665]

The heat riser has no effect on anything. Most of the time on something as old as we got they don't work anyways. Heck I havent had it hooked up on my blazer for years with no problems.