Anything to know about tuning up a TBI 305?

My truck ('88 GMC 1500) has been running like crap lately, and has recently developed a stumble right off idle, to the point that I can get it to die if I feed it abrupt throttle then back off quickly (which is not my normal driving style, just indicative of a larger issue, I feel). And it seems down on power - even for a 305, so you can imagine how underwhelming that is.

I get a feeling (specifically, a smell) that it's running really rich, though I haven't yet read the plugs to confirm that. I'm hoping this is also the cause of my 10 mpg return, and hoping to improve on that figure.

It's kind of a tired old motor at 167k mi, but I'd sure like to stretch a little more life out of it, since I'm in a serious self-imposed tightwad stage right now.

Any insights?

Mine had an issue with plug wires arcing to the heads, since the OE clips have long ago disintegrated, but I had more of a general intermittent miss when that happened.

I wonder if it's a TBI problem?

I'm wondering/afraid of that, too. I have just about zero experience with fuel injection, so I'm hoping that's not it.

the TBI system is brutally simple. there really isn't that much to go wrong. for your problem, i'd be looking at the plugs, wires, and cap and rotor. maybe throw a timing light on it and see where the timing is- they like about 10 BTDC. make sure you unhook the brown wire (either back by the distributor or under the dash behind the glovebox) before setting the timing.

Why is this in the off-topic discussion area instead of the grassroots motorsports area? I bet you'd get more responses over there.

I have no advice or potential solutions to your problem though, sorry.

I'd suspect bad sensors. In order, the MAP sensor, throttle position sensor, and oxygen sensor. Also wondering if you have a vacuum leak.

JeffHarbert wrote: I'd suspect bad sensors. In order, the MAP sensor, throttle position sensor, and oxygen sensor. Also wondering if you have a vacuum leak.

these are the steps I'd start with as well.

JeffHarbert wrote: I'd suspect bad sensors. In order, the MAP sensor, throttle position sensor, and oxygen sensor. Also wondering if you have a vacuum leak.

Vacuum leak crossed my mind.

I've noticed being choppy with the throttle at off-idle RPMs with the addition of brake application (like parking or other squeezing into tight spots) exacerbates the stumble.

A vacuum leak somewhere around the brake booster might have something to do with that, right?

Idles fine, stumbles when throttle depressed mildly, stumbles or stalls when throttle closes, then idle stabilizes? Test by pulling vacuum line off egr valve. Problem gone? Put a new EGR valve on it.

You have the symptoms right on. I'll check that out tonight, when at least looking outside doesn't make me start to sweat.