Jmyers224

Greetings everyone! (Thank you in advance for anyone's input)

I'm having some driveability issues with my 98 2.7 4cyl auto Taco. It is an intermittent issue. I'm getting rough idle and stumbling on acceleration. Everything is fine at first but after an hour or so of drive time, especially stop and go driving, the symptoms suddenly kick in. It begins to almost die accelerating from a stop. Almost as if the engine is being starved of fuel. It will crawl along at 1 or 2 mph when hitting the gas and the gas pedal will feel "dead", while at the same time stumbling and occasionally backfiring. After about 5-10 seconds it will suddenly "catch" and start accelerating. Once I'm up to speed it drives like a gem but will continue to act up whenever I'm accelerating from a stop. After the point where these symptoms kick in, the engine will also stumble and idle rough when in park. If I let it sit for a few hours the symptoms usually subside and I'm good to go until driving it for another few hours before they return. Whatever component(s) are at fault it most certainly seems (IMHO) that they are failing due to heat. The computer occasionally throws a P0172 (system to rich - bank 1) but no other codes have been thrown.

Here's what I've checked thus far:

1) Replaced fuel pump/filter.

2) Replaced spark plugs.

3) Checked plug wire resistance and also checked for arcing. Also checked the boots for hairline cracks. Everything looks fine.

4) Checked resistance on MAF. It was way out of specs, according to Hanes and AllData (it read 546 kilo ohms, manual says it should of been between 0.9-1.3 kilo Ohms @ 104 F). So I went to junkyard and bought used one. Did not solve problem. Checked resistance on used MAF and it also read similar resistance to original. Also checked the MAF on a friends same gen taco and his was out of factory specs. So, the testing procedures for MAF's according to Hanes or AllData are suspect in my mind (if anyone can confirm this discrepancy, please share). Also, checked that the signal voltage (back to the computer) fluctuates with throttle. In short, the MAF is not the issue. I reinstalled the original back on my truck.

5) Replaced Coolant Temp Sensor (the one for ECM, not the sender).

6) Checked TPS. Had smooth fluctuation throughout range (no dead spots or erratic jumping). Bought new one from autozone and installed anyway. Did not solve problem. Reinstalled original.

7) Had Midas (not my first choice but it was close by) do a computer diagnostic. Basically, Tech said that TPS checked out and o2 sensor was fluctuating nicely within range. He thought I had a MAF issue but I looked over his shoulder and saw and he was just reading the troubleshooting flow chart. Not much help.

8) Checked resistance of coil packs and camshaft/crankshaft position sensors. All were good.

I'm beginning to feel like this may be a computer issue. If anyone has any suggestions I would very grateful. I'm capable of carrying out electrical diagnostics if I know where to start, but am not sure where to even begin at this point. I do have an AllData account so if there's a procedure I should try I have that available to me.

j2the-e

Sounds like ignition. I would start with a compression test and if its good, I would replace the plug wires. Looking good doesnt mean anything. Resistance tests also don't mean anything unless a wire is completely broken. Fractured spark plug porcelain can cause similar symptoms. If a plug was dropped before install, even before you bought them, they can crack. You can also try swapping your buddies coils

Jmyers224

Hmmm, swapping out my friends coils? Why didn't I think of that, lol. Good idea. Ya, I suppose I should go ahead and replace wires as well and cover all my bases before I dive any deeper into this issue.

rokblok

iTrader: (1)

Have you checked and cleaned the throttle body with throttle body cleaner? The idle is controlled there, I believe, and if the butterfly is all gummed up, it can affect throttle response. I have to clean mine every 5-7K miles to keep it idling smoothly.