I just bought a used '92 Miata with 170,000 miles as a project. It's a 5 speed.Themotor seems to run very nice. No tapping or rattling, smooth acceleration in neutral. Sounds great.Here's the problem: When I'macceleratingthrough the gears the car seems to hesitate and and surge until I reach 4200rpm and then it pulls like a horse. During acceleration the engine sounds like it's firing properly and the rpm's increase evenly butthe ride is jerky and uneven. I changed the spark-plugs and wires. I replaced the fuel filter. I've run a tank of injector cleaner and I even sprayed the crap out of the throttle-body with throttle-body cleaner (but did not remove it, just sprayed the paddle anddown its throat). I've read a bunch of opinions on similar problems but most either don't hold water or I already tried them. I don't think it'sa weakfuel pump or it would get worse at higher rpm's... right? The O2 sensor has been suggested but I believe I would have a "trouble" light letting me know... right? The clutch is a little high but it seems to grab like it should. Anyone know what my problem is??? Besides not being smart enough to figure this out?! Thanks in advance!

 

Oh yea, one other thing. The timing belt has been recently replaced. I have receipts from the last owner. Seems he knew about the problem since some of the receipts include a fuel injector service and new plugs and wires (which I replaced again just in case).

 

Just discovered something on my lunch hour. It appears that if I push the gas pedal to the floor or close to the floor in 2nd, 3rd and 4th gearthe acceleration smooths-out. in other words, when I'm trying to accelerate at a mid-range rate by pushing the gas pedal about halfway so the rpm's will climb slowly, the car hesitates like crazy! I think it's an Air-flow-meter issue!!! Please let me know if this makes sense to anyone!

 

YIPPEE! I discovered what the problem was and corrected it! The car runs Fantastic now! Since I had so many great suggestions from this forum (0), and because I feel a little stupid,I was considering just keeping it to myself... But I'm just not that way! I mentioned that the timing belt had been recently replaced. It was done at a Muffler shop (mistake). After speaking to the previous owner again (he happens to work with me) I discovered that the car started acting up after that. Fortunately my car is too new to experience the dreaded crank problem that can happenwhen timing belts are replaced by "Muffler Shops".Armed with this new information I grabbed my trusty timing light andwhat do you know!!!... The timing was set WAY OFF!!! AARRGGHH!!! I turned the CAS (about an inch!!!) to the 12 degrees BTDC mark, reset the idle speed and TA-DAA... PROBLEM SOLVED!!! I'm guessing that since theTDC markis all the way to one sidethe mechanic at the "Muffler Shop" set the timing thinking TDC was in the center. Still doesn't explain turning it the wrong way. Maybe he didn't set it at all... Just did the belt replacement and left the timing where it was. Who knows.Thank goodness for Ebay because the AFM, TPS, ECUand Thermistor wound up costing me less than $150 total! None of them fixed the problem but the original ECU was pretty corroded from water on the passenger side floor at some point. I also replaced the fuel filter and ran about a gallon of fuel injector cleaner through the poor thing. The moral of the story is... START WITH THE BASICS THAT YOU LEARNED SO MANY YEARS AGO!!! Don't call the Dealer because he wants ALL of your money and will tell you anything to get it! Don't over-think!... And when you DO figure it out, pass it along just in case someknuckle-head like me is pulling his hair out trying to fix a problemhe should havelearned how to fix in"Mechanics 101"

Cheers,
John

 

I'v run into this problem before from a different direction. It is very easy to get the timing belt replaced incorrectly. It is quite common for it to be 'off' by one tooth as proper replacement has to be done with the belt under some tension. Changing the timing to correct the problem may damage your engine as the valves will not be opening in the right place to the crankshaft. To correctly fix it, the timing belt needs to be realigned correctly. It is about a 4 hour job when one does it by themselves. It isn't difficult but requires some patients.
Most of the running issues with this era of Miata are due to poor ignition. Changing to good spark wires and plugs often fix a lot of the foibles. On my 92' I had to replace the engine temp sensor (on the back of the block) at 132K miles and it is on its 3rd set of plugs and wires. 3rd timing belt. It didn't need replacement(timing belt) from wear as the old one had no visable wear to it even with 80K miles on it. At 141K miles it runs better than when it was new. Good luck.

 

I really appreciate the response! You're the only one on this sight that posted anything! That's OK though.

I thought about the belt being a tooth off but it's running so nicely now and the timing was set at almost exactly TDC before I adjusted it. I'm sure that's all it was. Bonus!... I'm now getting the 30mpg that the previous owner said it would get. (It was getting 23 to 25mpg when the timing was off)

 

Thanks "oneshot onekill", your exerience has fixed my dad's '95 miata. It was around Labor day 2008 when the he discovered that he was losing water due to a failing water pump. He and I have changed many water pumps in the past, but they were all on American made cars (GMC). While he did consider using a bottle of stop-leak, around Thankgiving he chose to take it to a mechanic friend. This was primarily due to the fact that the timing belt had to be removed. A day laterI took my dad over topick up the car with a new water pump and timing belt freshly installed. At the very first traffic light I saw him stall the engine when the light turned green. My dad has driven standard shift cars for around 50 years and I can't remember the last time he killed the engine by letting the clutch out. I knew something was wrong and we drove the car back to the mechanics garage. The next day the mechanic called and said the car was ready. When we picked it up, the mechanic said he checked it and nothing was wrong. As we drove away the engine was once again hesitating until it got woundup good. Back to the mechanic and this time my dad had the mechanic drive the car. Several minutes later they returned and the mechanic had convincedmy dad (at least temporarily), that this little enginehad to be woundup pretty fast before you used the clutch. After returning home, my dad knew the mechanic was wrong but just didn't know how to prove it short of reinstalling the timing belt ourselves. It has been a couple of months now, and my dad has tried various engine additives with no success, so I thought I would once again search the web for a fix. After reading your writeup, I called my dad (he lives 250 miles North of me), and told him to find his timing light and check the timing.With the timing belt linking the valve positions to the pistons and the spark timing linking the spark to the pistons, and didn't see how they related. How could the spark not be firing at the right time? Hours later I spoke to my dad and he said that the timing was way off and he immediately heard an improvement in how the engine ran as he shifted the CAS (Crankshaft Angle Sensor). I could not believe the timing was so far off with just a timing belt change then I remembered that there were two belt tensioners and that the CAS is actually looking at one of the cam shafts and not the crankshaft directly. Is it possible that more or less slack in the belt length from the crank cog to the Cas monitored cam cog could cause this? My dad doesn't much care, but he sure is happy that it is running like it did before the pump and belt change. Thanks for sharing your experience on this forum!

 

I wonder if this could be my problem? I have a 91 Miata with 160,000 miles on it. Only 3 owners, timing belt was changed at 123k and dring my last oil change I was told it was in good shape. HOWEVER, during my last oil change I was informed of a leaking valve cover gasket and had it repaired. Fastforward a month and my car starts acting up. Didn't start up right away, took about two to three tries. Then idled rough and acted like it wanted to die. It was idling between 500 and 600 rpms. Started making a very loud noise when I drove, mainly in the lower gears, and it was hesistating to accelerate into the next gear. The noise was embarrasing to say the least. Like a rice rocket, only the car wasn't moving fast at all. At stop light I had to keep my foot on the gas because i thought it would shut off

So I take my car back to PepBoys to see what the problem is and they say OOPS, the valve cover gasket we put in it was bad and it got oil all over everything, so we are going to replace the part and do your plugs and wires at no charge. Ok fine. WRONG. The give the car back to me in the exact SAME condition. I say, uh .. you didn't fix my car. What's up? They do another diagnostic and tell me that the camshaft position sensor went south because of the bad part and they replace that and give the car back. We get in it to do a test drive and AGAIN, it doesn't start til the 3rd try, and same thing, hesitating and rice rocket sound. The guy says bring it back tomorrow and we'll fix it.

Bring the car back the next day, they say its the coil and they replace that. I went and picked it up Friday night and lo and behold. NO CHANGE. I don't get it. (How they can continue to give me the car back in the exact same condition, and how they are NOT able to find the problem but just keep changing out random parts)

So before my boyfriend takes the car in for me tomorrow, i thought I would see if the world wide web could provide some answers. ANY help is GREATLY appreciated.