Running rough after motor mounts

[ambric]

This is odd, I know. I swapped in new motor mounts on my '99 two nights ago. Very simple. Unbolt, raise the motor a little, put new ones in. The next morning, it seemed to be ok when I started it, but by the time I got to work something wasn't right. It stumbled and hesitated at idle, but smoothed out once I got going. On the way home, though, it steadily got worse. It bucks and stumbles regardless of RPM. It sounds like it has a serious engine miss, but isn't throwing any codes. I crawled all over it last night looking for something that had come undone, but didn't see anything. I fired it up this morning and it's almost undriveable. Any ideas on what might have happened?

[jayjaya29]

Vacuum leak. Probably tore the intake boot/elbow when raising the engine.

[E85STI]

Vacuum leak. Probably tore the intake boot/elbow when raising the engine.

I want to second this. Depending on the age of the intake boot, it could look ok, but when it flexed while raising the engine it could have cracked. Or in the case of my intake boot, it was darn near ready to crumble away. My idle was horrendous.

When I took it off I noticed this.....

51619481674_82daa6ee19_b.jpg

[ambric]

No issues with the intake boot. In my experience, a vacuum leak will cause idle issues, but be less problematic as RPM climb (and throttle opens). In this case, it's regardless of RPM or throttle position. What it sounds like is a car with the timing waaay off. Like the timing has retarded so far that it barely runs. Is there something that could cause that?
M3 fb 7.jpg

[pbonsalb]

Ground cable on the passenger side mount?

[Rugbyfan]

When I went to solid mounts on my swap, the headers were hitting the front subframe ever so slightly. The above posters are probably correct, this is just something else to check.

- - - Updated - - -

Actually reading your post, yeah check that ground cable.

[blckstrm]

It sounds like coils to me. I don't see any cause/effect, but this sounds like how mine behaved when one of the coils failed. So it sounds electrical to me - that ground strap might be the issue.

[ambric]

It sounds like coils to me. I don't see any cause/effect, but this sounds like how mine behaved when one of the coils failed. So it sounds electrical to me - that ground strap might be the issue.

Did you get a misfire code when yours did that? I pulled all the coils and plugs last night and didn't see anything obvious.

[ScotcH]

- Hoses under the intake all plugged in?
- TPS plugged in (cable and plug not damaged?)
- pull each coil plug one at a time ... does the sound change for all of them?

[ambric]

Good suggestions, here. I'll try all of them tonight. Thanks.

[blckstrm]

Did you get a misfire code when yours did that? I pulled all the coils and plugs last night and didn't see anything obvious.

Nope, no codes. And yeah, there's nothing to see. If someone is close you could borrow a set of known good coils and test it fairly easily.

[Rugbyfan]

I thought of something else to check. If you were raising and lowering the engine maybe you induced an exhaust leak around the headers? That could cause the issues as your A/F ratio would be jacked up. It also would take a good amount of driving to throw a code.

[ambric]

It looks like BLKSTRM and ScottH are the winners in this... I pulled the coils one at a time. Every one of them bogged the motor except number 3. I swapped the #3 and #2 coil and plug and the problem stayed with cylinder 3. At this point, I'm thinking it was just bad luck that it happened when I swapped motor mounts and I have a bad injector on cylinder 3. Any other thoughts?

[ScotcH]

if the problem stays, that does seem likely! a bit more messy to change injectors than coils ... but short of a wiring issue or really low compression, seems like injector is the logical conclusion.

[ambric]

if the problem stays, that does seem likely! a bit more messy to change injectors than coils ... but short of a wiring issue or really low compression, seems like injector is the logical conclusion.

I thought the same thing. I checked and compression is 182-190 across all cylinders. I ordered an injector, since they're relatively cheap. We'll see...