ca18det misfire backfire under load
 

My det struggles to start, sluggish for a few seconds, then idles around 1100 rpm with a slight misfire, after a short while kind of after initial warm-up idles at around 800/900. When accelerator is applied it is misfiring and backfiring badly.

Things checked:

New plugs, gapped correctly
Coils swapped out
Maf removed and tested, working fine
Compression is 150 across the board
Ecu shows no errors, code 55. Did show detonation sensor but that is bypassed with a m ohm resistor
O2 sensor unplugged no difference
Previously checked the timing and was bang on

The car is at mot stage, just not running right

Any gurus point me in the right direction? I also think maybe my vacuum lines are on wrong but can't find a definitive guide anywhere

Have you checked the fault codes on the ECU, are the plus/coils firing properly?

any cracks in or boost pipes off ? fuel pressure reg, fuel filter blocked, injectors,spray carb cleaner around inlet manifold gasket and around boost pipes, see if the revs go up.

All codes are clear on the ECU, it did have the knock sensor error, I've gotten a fresh length of shielded wire and wired it up, that code is gone and it ran a bit better.

Boost pipes seem ok but I haven't properly tested for leaks with a compressor etc. Tried the carb cleaner around the piping, no change.

I did speak to Elliot who I bought my Mk1 from, he had an s13 det he told me to bypass the boost solenoid and go from the back of the intake straight to the FPR, misfires a lot less. Still feels like a small misfire on idle but no where near as much. Misfire is only there on acceleration at around 1200 - 1500 rpm. After that it's sweet.

EDIT: Oh yh, it's now MOT'd. Passed with flying colours no advisories!