Hard cold start despite new idle air control and fuel pump replacement

97 Tacoma has been getting harder and harder to start up when cold. I’ve recently replaced my idle air control with a new one from TRQ to try and help with my high idle problem because my old iac was getting stuck closed , the new one did help bringing the idle from 2000rpm down to around 1400rpm warm idle which is still pretty high I know .. but that’s not the main problem. Since replacing the IAC my truck has a hard time starting from cold start . The first crank misfires almost and the second crank starts the truck but it sputters trying to climb up the rpm’s

when it does eventually start the truck runs normal (besides idling high ) and starts up right away when the engine is warm any other time . I’ve replaced things recently such as the fuel pump and fuel filter . I’ve looked for any vacuum leaks but am unable to find any

Could this be an air related issue ? Or a fuel issue ? Battery is fine I’ve checked voltage and even with a jump pack the truck does the same symptoms . Could the iac cause this hard starting ? I do have to mention my cold air intake is rlly old and the filter is rusted and crinkly but the truck would have this problem maybe once a month with my old iac but now it’s every morning and after work the truck has a hard time starting up . Could it also be a starter issue ?

 

How many miles on the truck? Ever run a compression test? Have you inspected spark plugs?

 

@Red_03Taco 300k and I haven’t done a compression test neither have I inspected the plugs I’ll probably do that today

 

Ok I would suggest doing those and updating us on how those check out. Low compression could certainly cause rough cold starts or no-start conditions (and as things heat up, compression usually improves).

Plugs could also be a problem themselves or may smell like fuel if perhaps a leaking injector is your culprit.

 

not sure what a TRQ IAC is but if it's not 100% Toyota OEM you'll have problems. Have learned this the hard way. knock off IAC's are completely different inside vs the OEM. Either way cold hard start wouldn't normally have to do with the IAC. I'd check spark plugs and make sure you have the correct dual electrode ones if your truck calls for it. Ck spark plug wires and coils to make sure you're getting good spark. As for fuel i'd go back and double ck to make sure you did everything right on the fuel pump swap. sometimes a small mistake like a disconnected vacumn line makes a big a deal. Does it throw any codes?

 

@hessian42 true I knew what I was getting into not getting a oem iac, and this truck I’m unable to read codes always had been since I’ve had it lol. Been too busy to work on it but both of you guys gave me and idea of where to look. I’m starting to suspect injectors but before I do any of that I’ll start with the basics and check compression, plugs , and any loose hoses fuel related

 

I'd put injectors down the list a bit. If the engine is running smoothly after you get it started, its probably not the injectors. Compression test will tell you if low compression is a factor.

 

Agree that compression should be checked first. But injectors can leak while the motor is off and create a rough start situation too, then the motor can smooth out afterwards

 

That's certainly possible. The OP says that the motor starts normally when it is warm, which would be after any leaking fuel has been resolved, but that the hard starting problem first appeared after the IAC was replaced (without any change in the injectors). I'd put injectors on the possible list, but not on the top

 

Hey everyone. So I ended up finding 3 of my injectors were leaking , the little rubber o rings were all messed up . I didn’t have the money for new injectors so I replaced all the orings on all 6 injectors and now my truck isn’t leaking anymore or smelling like gas and starts right up . But now it’s doing something else … my exhaust is starting to back fire when letting off the throttle either just reveving it or while driving , it’s like surging almost .

The truck isn’t misfiring or out of time, so now I’m wondering if my injectors have just been leaking for a while and now that it’s sealed again , do I just have to run the truck and see if it fixes itself or clears whatever pressure it use to have ? Just a small thing I’m wondering about, the main hard start and smelling like gas problem is fixed rlly appreciate your guys help

 

Go check your TPS with a multi-meter. Perhaps the issue will fix itself, but I'm a bit doubtful of that. I helped a buddy install new used injectors and a TPS and it solved a surging he had under acceleration between 2-3k rpm. Because we did TPS and injectors we'll never know which one was the solution. But apparently a slightly clogged injector could cause surging (that's why we replaced his). So maybe you could try some injector cleaner in your next tank of gas as a cheap shot in the dark solution.