D15z1 low idle and miss

[Onedopehatch]

I have a 92 civic cx that was swapped with a z1 (previous owner). When cold it idles around 1000rpm and is smooth at idle but once it warms up it idles on the peg (below 500) and misses. Also every once in a while, while I'm driving in first or 2nd at around 2k it'll bog out for a few seconds and if I hold my foot at the same throttle percentage it'll pick back up and take off like a bat out of hell without me giving it anymore gas. I've already cleaned the iacv and it didn't change anything. Could it be a vacuum leak somewhere? Any help is appreciated

[PaleMelanesian]

Check for cracks in the exhaust manifold. When mine cracked (right at the O2 sensor) it would vary between low stumbling idle and surging to 2000 rpm at idle.

What's your fuel level? Mine would stumble when it got low, well before Empty.

[Onedopehatch]

I fill up every Monday and its usaully around 1/2 tank. I'll check for cracks but it doesn't sound like its cracked at all

[litesong]

Originally Posted by Onedopehatch

I have a 92 civic cx that was swapped with a z1 (previous owner). When cold it idles around 1000rpm and is smooth at idle but once it warms up it idles on the peg (below 500) and misses. Also every once in a while, while I'm driving in first or 2nd at around 2k it'll bog out for a few seconds.....

My 88 carbureted Ford Festiva also had a few misses at idle & bogged down in 2nd gear while ascending our moderate hill to our home......while using 10% ethanol blends, E10(all brands). Switching to ethanol-free gasoline(E0), Festiva is wonderful, with no bogs, or misses & now has excellent response.

There is a major difference between E10 & E0, & why auto forums don't delineate the differences more often is beyond me. My later fuel injected cars(2007, 2008, 2013) don't have the performance problems of older cars while using E10, but show E0 mpg increases of 8%, 7%, & 5%.

87 octane low compression ratio gasoline engines are tuned for 87 octane E0(duh). However, 87 octane E10 blends have very few of their molecules that ARE 87 octane. First, ethanol is 114 octane, way out of the design parameters of 87 octane gasoline engines. Second, to balance the ethanol octane, the remaining GASOLINE molecules must average 84 octane. Again, outside the parameters of the 87 octane gasoline engine.

It is amazing that mpg differences aren't greater than I report. Some drivers DO report greater E10/E0 mpg differences.

[Onedopehatch]

I do run e10 in mine, most gas stations only have e10. I'll try running e0 my next fill up and see how it goes

[Onedopehatch]

The car is also not running on a p07 Ecu witch I believe is what vx's should run on correct? How much do you think that effects fuel economy? I know it dosnt go into lean burn or vtec with the current Ecu

[California98Civic]

The CX had the b8 engine and the VX had the z1, and if you don't have the matching ecu and wire harness then it might behave quite strangely. The CX had the p05 and the VX the p07. I don't know if that is what is causing what you are facing. Does your car have the z1 wiring harness? It would be a little different, I imagine.

[Onedopehatch]

I didn't do any of the swap, but I am pretty sure it's the cx harness considering vtec isn't hooked up and it doesn't have the 5 wire O2 sensor

[California98Civic]

I think your first step should complete the swap: harness, ecu, proper O2 sensor.

[Onedopehatch]

I've been searching locally and haven't been able to find any of the parts I need. I'm gonna have to look on eBay or somewhere else