Throttle hesitant

[Jakethesnake]

So I have a 90 na and when I start the car to go anywhere it had very poor throttle response . Only while it's sitting still does this happen . If u tap the gas as if you were pulling away it hesitates very badly . Now when I'm driving the car it seems to run fine . It doesn't skip or hesitate . What could this be? Where should I start. The car is basically stock . Only mod is cat delete . Still has factory muffler and exhaust. Help please

[kung fu jesus]

Does the power bog, then come back around 3000 rpms or so?

I don't want to be alarmist, but because of the year your car is, I immediately think "crankshaft nose issue", but I it could be a other stuff too. I just need a better description or details of the issue. Can you video the crank pulley at idle? I am asking this to see if it wobbles. It's down at the bottom of the engine, up front. It isn't well lit, so using a flashlight to illuminate it helps a lot.

Other things could be far simpler, like plugs and wires, poorly set timing, but before throwing parts at it, I am trying to streamline the symptoms to get to the issue.

You could also put a timing light on it and see if it is jumping around a lot, too, at idle.

[Jakethesnake]

I hve a timing light and I have experience when it it comes to engines and car but this is my first miata so I havnt learned a lot yet about them . I was big into Hondas for about 6 years .

[Jakethesnake]

The guy before me put a timing belt and water pump on the car so I'm thinking it's a tooth off timing . And the car clears up at higher Rpms . It's just very hesitant if u tap the gas quickly it doesn't respond from idle

[kung fu jesus]

It is possible. The crank nose/keyway issue reacts the same way, though. A botched timing belt job causes the woodruff key to round out the keyway on the nose of the crankshaft, so the timing belt cog on the crankshaft slips or shifts a little, acting like the timing is off. All is not lost, though, there are repairs for it.

Again, this is worst case scenario stuff, but it is what I would look at first. I am distrustful of previous owners I do not know, so while he may have in fact done the timing belt and waterpump, he may have also discovered the keyway was fubar'd and sold it. This is only conjecture, but just my reaction based on your description. It could just be in need of a tune up.

[Pyr0monk3y]

I've been chasing a similar issue for a while. What improved my situation greatly was a new fuel pressure regulator. I would save that for later though. The usual suspects for hesitation are spark plug wires, spark plugs, fuel filter, and O2 sensor.

A fuel filter is something that should be done to a newly purchased car anyway, so go ahead and do that. Next, try new plugs and wires. Plug wires don't last very long on these cars and if your wires aren't blue and made by NGK, they are likely crap. Even if they are blue and made by NGK, you're lucky to get 15k out of them. Next, replace the O2 sensor. $45 will get you one with an OEM plug. <5minutes to swap it. If you're still having trouble, don't feel bad about wasting money. Your car was going to need all of this stuff sooner or later. Now it's time to get more serious and look at the fuel system. This includes the fuel pump, fuel pressure regulator, and the fuel injectors.

I'll stop there because that's where I'm at. Good luck.

[Jakethesnake]

Thank u fellas . Helps a lot I will try these few things . Now as for the key way .. How would I go about checking this?

[kung fu jesus]

Well, the timing jumping around after it's warmed up at idle is one clue, but you would have to remove the timing belt, pulley and cog to see. At that point, it would be a good idea to have a new woodruff key and crank bolt on hand to replace them. The crank bolt on the nose of the shortnose will stretch, IIRC, at the factory torque spec.

[Jakethesnake]

It it always does it at idle and pre take off. After u take off it's back to normal

[kung fu jesus]

Yeah, you have quite a few leads to follow above, time to see it through for a proper diagnosis.

[Satisaii]

The rubber bit on the harmonic damper can separate and cause erratic timing readings. You could turn the inner and outer rings by hand on the one off of my 91. This would have no effect on the way the car runs, but makes it very hard to set the timing.

I am with KFJ on the not trusting the PO work with a potential short nose crank engine.