Bump at ide--Trans or engine related?

[jgr]

Help.

I need some advice about what might cause a quick bump. The entire truck will shake and the engine will quickly rock. I'm not sure if it's trans related or engine related. It happens at full operating temp, in gear when sitting at long stop lights. There doesn't seem to be any pattern as to when it will happen.

The engine is completely tuned up and then some. Cleaned MAF & ICV, new plugs, wires, fuel filter, and etc. I also checked the ignition coils. The engine runs smooth, RPMs are steady except for this random bump. Should I be looking for something like blown head gaskets, bad injector, bad trans....?

Thanks

 

[LINY4Runner]

does this happen as you're coming to a stop? Could be the driveshaft slip yoke if so...

 

[jgr]

This is at a complete stop so it rules out the slip joint on the drive shaft. It's such an abrupt bump it almost feels like another car tapped my bumper. Most of the time the tach doesn't even indicate anything happened.

 

[LINY4Runner]

that's tough, can you narrow it down?

try and isolate when, where and how the sound happens. these details are imperative to the diagnosis, because at this point it can really be anything...

 

[Stick Figure]

if it helps, i know what your talking about, but i have yet to figure out exactly what the issue is. Does feel exactly like someone just bumped into the back of you though.

 

[Glockwarrior]

My wife's Corolla does that....its like someone had bumped you from the back, in some cases even feels like your lurching forward.
I have always been curious about that.
(I know this is a 4runner forum):biggrin2:

 

[juiceboxer]

My guess is it's the A/C compressor kicking on, causing a larger draw on the motor, which tells the ECU tro bring up the RPM's and you are noticing that jump. Unless it happens with the A/C off...

 

[jgr]

Happens after coming to a complete stop and will begin to happening at random time intervals. It's almost like a backfire with out the noise so I'm guessing it's a misfire. It occurs less frequently when it's in park.

It will do it with the AC off but it is more frequent with it on and it's way worse than a normal AC compressor kicking on.

Could this be a leaky injector and is there a way to test for one?

Suggestions welcome.

Thanks.