Weird engine behavior?

[E30_Narek]

So for the past 2 weeks I've been experiencing this problem. On a cold start, my car's idle alternates for a few seconds from 600-1500. It settles after a while but it moves up and down every once in a while. Sometimes when downshifting and I try and rev match, the car won't rev and the check engine light will blink for a split second. Sometimes when driving the car "hesitates" upon acceleration and the RPMs drop and shoot back up again, causing a kick or a stutter when driving. Again, the check engine light flashes for a split second as this is happening. I did the stomp test and the code was 1215, which is the AFM. I changed the AFM and the problem is still here... but worse. What else could the problem be? Vacuum leak?

EDIT: I checked my intake boot (as I heard that's a common area for vacuum leaks) and noticed there's a crack or tear about an inch long on it. It doesn't seem like any air could escape from that as it's only on the surface, but could that be it? The problem seemed to get worse after I fiddled with that.

[dnguyen1963]

Have you ever heard of smoke test?

[AndrewBird]

An inch long crack will definitely cause problems. Start by replacing that and also look for other leaks. A smoke test would be a good idea.

[E30_Narek]

Have you ever heard of smoke test?

Yes, I've heard of a smoke test. I just don't know where to get the supplies to do it.

[AndrewBird]

Well, you either take it to a shop that has a machine, or you build a machine yourself. You need an air compressor though if you are going to do it yourself.

[efficient]

Google diy smoke machine or youtube

[E30_Narek]

So I changed the intake boot and for some reason my car is worse than ever. As soon as I turn it on... it almost dies out, but saves itself. It's idling between 300-400 and it doesn't rev past 2k.

[dnguyen1963]

Disconnect the negative battery cable to reset the ECU. It will take about ten min for the ECU to adapt to the new conditions.

[E30_Narek]

Disconnect the negative battery cable to reset the ECU. It will take about ten min for the ECU to adapt to the new conditions.

Did that, check engine light turned off. Did a stomp test and the code came out to be 1444 which means no faults. I also put my old AFM on and it is running better than it was previously. But the idle is still surging, it takes a long time for the car to start, there's a smell of fuel coming out of my exhaust, and the car stalls if I tap the gas.

[dnguyen1963]

Apparently, you cannot drive your car to a shop to get smoke test done so I highly suggest that you look up a DIY for making a smoke machine. Until you can rule out vacuum leaks, you might be chasing your tail.

[E30_Narek]

Apparently, you cannot drive your car to a shop to get smoke test done so I highly suggest that you look up a DIY for making a smoke machine. Until you can rule out vacuum leaks, you might be chasing your tail.

I'm pretty sure I can somewhat drive the car. I'll just do the best I can to take it to a mechanic and have him work it out.

[EatsHondas]

E30's run like absolute shit with vacuum leaks on factory engine management. You can smoke the engine for leaks with your favorite tobacco product, a few feet of tubing, and a rubber glove. I'll describe what I did.

Remove the airbox and AFM, and seal the end of the intake boot with the rubber glove. Poke a small hole in the glove and insert your tubing. Keep the hole small so it will stay sealed with the tubing poked through. Stuff shop rags or equivalent in the exhaust to contain the smoke. Prop the throttle body wide open. Proceed to collapse a lung (blow the smoke into the tube) into the intake through the tubing. After you fill the intake and crankcase with smoke, you will almost be guaranteed to find most of your leaks.

I found the cause of my lumpy idle with this cheap, ghetto-fabulous method. The biggest of the leaks turned out to be a worn throttle blade shaft. Over the course of 25 years, the hole wallowed out enough to allow the engine to breathe through it, causing it run erratically (too lean).

Don't take it to a mechanic man, teach yourself something new!

[AndrewBird]

Sometimes new intake boots come with a plastic plug missing. This creates a giant vacuum leak. Check that first. If the plug is missing, you can pull the one out of your old boot.

[E30_Narek]

Update: well turns out I had no vacuum leak. It was my stupid fuel filter all along...