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Old 02-08-2013, 03:43 PM   #1
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Default 1999 Miata, Low RPM hesitiation

The car is an almost stock 1999 Miata. It has an aftermarket intake, and has a terrible low rpm hesitation. Also you can sometimes hear backfires through the intake. The timing is good, and the check engine light is not on at the moment. At one point, it had a code p1345, for cylinder discrimination signal (camshaft position sensor). Nothing has been replaced yet, besides new plugs, wires, and fuel filter. I'm working on it currently, but some different point of views would be very appreciated!
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Old 02-08-2013, 06:01 PM   #2
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check cam timing, has it been touched recently.
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Old 02-08-2013, 06:14 PM   #3
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It has not been changed since I have had the car
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Old 02-08-2013, 08:03 PM   #4
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Could be a number of things.

TPS, throttle body, idle air control, DOA wire or plug, cam sensor, crank sensor, MAF, coil pack.

Any one of these can be going out or giving a crappy signal. I have personally had two DOA crank sensors,one OEM and one AM also one DOA plug wire, NGK.

The crank and cam sensors aswell as coil pack on the 99/00 cars are known to be problematic.

When does it happen? Lite throttle not moving, in fifth gear, first..? During over run too?
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Old 02-08-2013, 08:36 PM   #5
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it happens in any gear, above light throttle. If I roll onto it, it's okay, but it's barely enough to get me started on hills. I was wondering if this could be coil pack related. Fuel pressure is at spec, and compression is good, btw. i cleaned out the injectors also.
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Old 02-08-2013, 09:23 PM   #6
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Check for spark on all wires.

What do you mean by "cleaned out the injectors"?
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Old 02-08-2013, 09:29 PM   #7
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The cam position sensor is easy to change out on a '99 and is under $50 if I recall correctly, but I'd expect the car to throw a code more than once. Same with coils; I'd expect to see a random misfire code or something.. Is it possible you have a vacuum leak? That can cause the symptoms you describe and not be flagged by the ECU. Maybe something's come loose in the intake tract and it's getting a bunch of unmetered air?
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Old 02-09-2013, 10:42 AM   #8
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I removed the injectors from the rail, and used shop air and brake cleaner to clean them.
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Old 02-09-2013, 10:45 AM   #9
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If there was unmetered air coming in, wouldnt it throw a lean code?
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Old 02-09-2013, 10:55 AM   #10
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Check to ensure the maf sensor is installed in the correct direction.
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Old 02-09-2013, 11:09 AM   #11
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It is installed correctly.
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Old 02-09-2013, 11:18 AM   #12
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Quote:
Originally Posted by AredMiata View Post
If there was unmetered air coming in, wouldnt it throw a lean code?
I don't know, although yeah, you may be right. (Does the ECU look at the O2 sensor at idle? And if so, isn't it striving for the leanest mix possible for emissions? The Factory ECU is a mysterious land of many questions for me..)

After reading the cleaning method used, I'm wondering if maybe an injector pintle was damaged in the process and is now leaking? Maybe a leaky injector seal? In my experience a car that idles and tips-in like crap but cleans up with revs is either pulling air/losing vacuum, or just loading up on fuel.

Spray a can of carb cleaner around the intake and injectors while its running (or use a propane leak sniffer like mine) and see if the idle changes. If it does, you're leaking there. It'll only take 5 minutes to rule out.
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Old 02-09-2013, 01:17 PM   #13
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If he was leaking vacuum and or air the idle would be higher than normal and probably fluctuate up and down too.

Have a few friends over. Put one spark plug wire in in each of their right hands. Crank the car over and see which one doesn't jump and scream. Could be two. Reward with beer.

Also, check the codes with a reader. Codes can and will be stored but not show a CEL.

I've still got my money on sensor(s) or coil pack.
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Old 02-09-2013, 11:24 PM   #14
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Already checked for pending codes. There were none. Rechecked timing today, took all the front covers off, timing is definitely spot on. Noticed a bit of pulley wobble though.
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Old 02-15-2013, 08:42 PM   #15
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Quote:
Originally Posted by AredMiata View Post
Already checked for pending codes. There were none. Rechecked timing today, took all the front covers off, timing is definitely spot on. Noticed a bit of pulley wobble though.
Crank pulley wobble is probably not good, although I'd expect it a lot more in your '90 (small-diamater short-snout 1.6 crankshaft) than in the '99.

Just curious; does the pulley actually look like it's wobbling on the crankshaft, or is it possible that something got bounced/wedged up in there and bent the lip of it (and in doing so possibly dislodged/damaged the crankshaft sensor)?
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Old 02-27-2013, 02:19 PM   #16
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The crank pulley is wobbling. Some more info that may be useful; my friends said during a rather spirited cruise, the exhaust under the car was glowing red. There continues to be no codes, no cel. This is so aggravating.
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Old 02-27-2013, 02:31 PM   #17
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Is this another clogged cat issue?

I remember another thread about this where I believe brain included pictures of his cat Red hot. I don't rememeber the symptoms though.
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Old 02-27-2013, 02:42 PM   #18
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Glowing exhaust on a mostly stock car is going to be a clogged cat.
Reason why it is clogged would likely be a bad a/f mixture, possibly caused raw fuel making its way out the exhaust due to bad CAS or coil pack...you have more than one problem imo.
Cut the cat out and see how car drives. Then find narrow down what is causing your miss before you weld a new cat in.
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Old 02-28-2013, 12:03 AM   #19
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Well the cat is not clogged. I took it off and ran the car down the road. If anything, it was worse.
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Old 02-28-2013, 08:14 PM   #20
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you said pulled off the cover and checked the timing. did you check the cam timing , spark or both? One tooth off may be difficult to see when viewed from above.. injectors..I have seen a few of them be put back in after someone "cleaned them" and failed to lubricate the o-rings while re-installing them. they get shoved into a sharp edged hole, all dry and they get shredded. the obvious clue on that one is the dumping fuel though. kinda hard to miss.
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