rbh261

I have a '98 3.4. It has a slight rough idle that I feel mostly through the steering wheel. It it usually fine until the engine warms, then I notice it. I have cleaned the MAF and throttle body. I have replaced the plugs (NGK) and wires. The oxygen sensor has been replaced as well as the fuel filter. I have even put the original wires back on. Have checked all plugs for cracked insulators. Checked for vacuum leaks.

I used a timing light to check for a possible misfire. When hooked to each wire I get the same thing. The light blinks steady then skips. It does this on each individual wire. If I actually check the timing with the light, the timing is jumping in advance when this happens.

I'm thinking crank sensor or cam sensor, but I have no reference for thinking this. I'm hoping to get this thing on a scan/diagnostic tool soon. I have a friend with laptop equipped with an advanced diagnostics porgram. Hopefully I can pinpoint the problem that way. Until then, I'm open for suggestions.

4Runnerman

I have a '98 4Runner with the 3.4 and have the same problem I tried the same things (new plugs, wires, O2 sensor, fuel filter, cleaned MAF and throttle body, checked for vacuum leaks, etc.), but I have yet to resolve it or receive any helpful advice.

I'm wondering if a coil pack is going bad.

Please let me know if you figure it out because they definitely shouldn't run this way.

THANKS!
John

Alexander 26

i think it's common "problem" for all 3gen 4runners. mine has been doing the same thng since the day i bought it. 4years ago. forget about it.

Quickdraw

Check coils packs and the spark plug connector boots. I had same problem, coil packs were good but spark plug conn. boots were all corroded and tore up (after 11 years of use) and the spark would sparodically jump down the side of the spark plug.

rbh261

Good news, I think. Yesterday, a friend and I ran advanced diagnostics with a laptop. No codes pending or stored. The ONLY problem we could see was that the ECM thinks the engine is running at 221 degrees. The gauge was normal and the engine actually temped normal with a temp gun. We also noticed the timing hunting around up toward 20 degrees BTDC and a rich condition at the o2. The ECM is trying to cool the engine down with timing and fuel. I'm going to get a new temp sensor today and will install it in the next day or two along with a thermostat to be safe. I will let you know what happens.

rbh261

Changed thermostat and coolant temp sensor today. So far, everything is running very smooth.

rbh261

Can the boots on the coils be replaced without replacing the coils?

mkgarrison5

thats what i was thinking.. its a TRUCK not a mercedes

mkgarrison5

unless you are being jolted around i wouldnt worry about.. get decent gas mileage?? if so no worries..

MTL_4runner

The boots are not sold seperately to the best of my knowledge, but you can use some dielectric grease for using on the boots. If they are bad enough, just buy a new coil pack (or get a used one from a boneyard).

NMoffroad

rbh261 please keep us updated, is your vibration still gone, I know it hasn't been too long but, my 97 does the same thing (i think) and I would like it to run the best it can, not forget about it. Also, what computer diagnostics program do you have, what did it cost and where did you get it? thanks

MTL_4runner

It was likely a BR-3
http://www.obddiagnostics.com/

or an Auterra
http://www.auterraweb.com/

rbh261

The diagnostics equip looked like the one in the first link. I'll have to ask my friend which one he has. He uses it on a '96 Trans Am LS6. It allows him to disable certain sensors and such. He turned off his o2 sensors behind where his catalytic conv. used to be. He is installing a 6 speed in place of his auto, it allows him to use his current ECM and PCM with the 6 speed. It's a pretty awesome setup.

So far, the vibration is still gone. It does it a little when the rpm's drop with the truck in gear at a stop. It idles at about 650k when this happens, so I'm not worried about it in these circumstances. At normal idle, it's just fine now.