A new problem (at least for me) just came up. Did an engine swap. It is a used engine, recently rebuilt by mazda. It ran perfectly fine while it was in another car. After the swap i found a cracked fuel line on the motor going to the injectors, so I replaced it, ended up removing both fuel rails with injectors to reach the line. Anyway, current problem is that the engine turns over but does not start. It takes countless attempts at cranking until it fires up. After it starts I have to raise the rpm a little for a few seconds to keep it from dying, after almost a minute, it runs by itself, without my input, but it always idles around 1500rpm, and after a little while, when it starts to warm up, it starts 'hunting', idle begins to surge. I checked and replaced all spark plugs and all 4 are firing, fuel appears to be injected. However, when it warms up, I can shut it down and re-start it with no problems, except for the 'hunting' issue. I also checked the tps and it is in spec, replaced the wax rod. I'm running out of ideas. Any input will be greatly appreciated.

P.S. I did use the search option, but I couldn't find a solution.

 

Idle Speed Control Screw, Idle Control Screw (on TB), are you running a stock ECU?,

 

Start with the stuff you messed around with to fix your first problem. Your culprit is bound to be something that was tampered with.

 

ecu is stock, I have another stock one, so I tried swapping them but nothing changed. I loosened all the idle control screws on the front of the throtle body (closer to the front of the car), so that the plates are completely closed, I didn't touch the screws on the back of the tb (closer to the fire wall) since the motor was working fine while it was in another car, this side was never touched. I wa tracing back everything I messed with, removed the uim and everything appears to be in place and ok, all of the vacuum lines and electrical connectors are connected, no kinks in the fuel hoses going to the fuel rails, all 'grounds' look ok. Another thing I discovered is: I cranked it may be 20 times in the morning and it didn't start, so I started tracing back everything I touched and removed the uim, there was no smell of fuel coming from the intake manifold, however when I connect fuel pump to ground in the diagnostic box and turn ignition on, injectors are making noise, so I assume they are working, but there was very little fuel smell from the intake after that. After I put everything back together, and another 20-25 attempts it finaly started again but with the same symptoms as I described in the first post...hunting, etc. although it was marginally better. I'm completely out of ideas at this point