SR Poor idle, bogs/loses power at cruise

[JoshDank]

So, I can't seem to figure this one out. I have a s13 sr tat runs great and makes good power under acceleration and wot. The problem is the idle seems to fluctuate quite a bit and the car bogs hard at cruise and light throttle. She comes right back to life if I mash the gas. I thought it was a bad tps (dead spot), but I checked voltage and it seems to be reading proper through the entire range.

I've played with the iacv and it helped the idle, but it's still not quite right. I've checked timing as well. These may be two separate issues, but I don't know what else to check. Any help would be appreciated.

[JoshDank]

Anyone have any suggestions? Any more info I can provide?

[codyace]

Vacuum leaks
BOV recirculated?
Timing via Light/Consult

[2402NV]

Have you changed your plugs?

[JoshDank]

The engine only has ~2k miles on a fresh rebuild. I bought the car and it's been doing this since the engine was installed. Plugs are good, checked timing with a timing light, bov is not recirculated, but I was running the same setup on my last SR with no issues. I can't find any vacuum leaks, and vacuum holds steady while at idle.

It doesn't feel like it's breaking up, just cuts all power at cruise until I push past about 40% throttle.

[codyace]

what management are you running?

[JoshDank]

Stock SR ecu

[codyace]

If a stock computer, I'd really just go back over and check for all vacuum leaks that you can. These cars dont usually develop a wondering type (ie: honda) idle unless a huge vacuum leak or a timing difference.

FWIW: Unrecirculated BOV is never good, and is never right. Works doesn't mean works well.

And you said you did put a light on it and verified 15* right?

[JoshDank]

If a stock computer, I'd really just go back over and check for all vacuum leaks that you can. These cars dont usually develop a wondering type (ie: honda) idle unless a huge vacuum leak or a timing difference.

FWIW: Unrecirculated BOV is never good, and is never right. Works doesn't mean works well.

And you said you did put a light on it and verified 15* right?

Yea, had to adjust the cps when I bought the car, but we got it back to 15-16*

I'll go over all the vac/boost lines again.

[JoshDank]

Ok, can't find any vacuum leaks and the bov is now recirculated. I found that the previous owner had the idle adjustment screw set so that the throttle body butterfly was cracked open too much. I fixed it and now my tps seems to be reading perfect (.45 volts when closed). The idle is better and stays right where it should when I first start it up. However, as soon as I drive it and come to a stop, it slowly idles down until it wants to stall, causing me to constantly play with the throttle.

I'm less concerned about the idle than the cruise issue though. Like I said before, acceleration and WOT feel great, but as soon as I get into a cruising state, she seems to lose power. I watched the vacuum/boost gauge and it seems like as soon as I get past 0 vacuum she comes back to life. I'm totally confused...

[codyace]

What sort of vacuum does it pull when ideling and at what rpm does it idle at?

The breaking up under low vacuum is perplexing to say the least without being there with the car

[JoshDank]

She's idling around 1k rpm now and pulling ~20 inHg

[JoshDank]

Well, I've fixed the issue and figured I'd post in case anyone searches and finds this thread. I tried changing the ECT sensor and took a spin around the block, but the problem was still there. I finally decided I'd try pulling the o2 sensor plug and now she runs like a champ. Apparently the oxygen sensor was giving bad readings and screwing up afr enough to choke the engine.

This makes sense since the car felt great when in open loop (not using the o2 sensor readings). Looks like I'll be replacing the o2 sensor... at least it was nothing too major or expensive.

Thanks to those who helped.

[codyace]

Nice diagnosis! Once I read that you were pulling good vacuum, that reall helped eliminate much of the issue. What is even more interesting is that a faulty o2 typically throws the car into limp mode, regardless if in closed or open loop.

Chalk this one up for the boards!

[JoshDank]

Agreed. I was surprised by the solution. Appreciate your help!