1990 1.6 misfire, won't rev past 3.5(ish)k, sometimes struggles to start

Hi all,

I had a new engine fitted, about 8 months ago. Only done about 500 miles in that time. But ever since its a stutter misfire, sometimes it never happens. But today was really bad. The symptoms are:

  • Regularly wont rev past a certain revs. Sometimes 3.5k ish (today) sometimes 5.5k ish. Basically it wont go to the red line ever.

  • When the this happens, the rev needle bounces around like mad. Hitting 0 sometimes.(something to do with the igniter??)

  • This morning it really struggled to start. Took 3 attempts. (this rarely happens)

  • I’ve changed the tps but no better (maybe even worse)

I’m going to change the spark plugs today to see if that helps.

Any help would be great as its very annoying!


Might be the Mass Air Flow Meter MAF needs cleaning but only use a suitable MAF cleaning product nothing else, but first check all the fuses I don’t remember the number check them all but look for a 15 amp and if not check the relays…
Check online to see which one controls the TPS.

Spark plugs look like this after 500 miles…running rich??

ok great, thanks, i’ll give all that a try

MAF on a 1990 will be a flappy type not a hot wire. I’d suspect the engine coolant temperature sensor from those symptoms. It’s the 2 pin sensor on the back of the engine under the coil packs.

Ahhh good idea! thanks. I have just bought one on MX5 Parts and all the reviews said how it fixed cars with the same symptoms as mine, fingers crossed!

similar problem a while ago where the engine would stutter at high revs or not start when warm (e.g. 15 mins after turning off). lots of suggestions online about plugs and leads but replacing the ignition coil worked for me and no problem since. A common MX5 problem it seems. Really difficult reaching the lower bolt though!

Just to let you know that this had worked! Thanks!

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Thanks for the feedback :+1:t2: