1990 NA6 hesitation & feeling sluggish [Archive] (2024)

FlavouredMilk

23rd June 2015, 18:46

Okay. So I'll open with a disclaimer, I have tried browsing for the answer, but I don't trust throwing parts at my car based on someone else's problems and I'm also on my mobile, so browsing for answers isn't easy. I apologise for not being able to track this down.

Right, so I am the proud owner of two lovely NA6s, a '91 (268,000km) and a '90 model (188,700km), the second of which I have only had for a few days. I serviced it yesterday, throttle body clean, injector clean (tank additive), new spark plugs (BKR6E-11, I'm aware 5s are better but I was using shelf stock) and new oil and filter and after starting the car up to run the fresh oil through, I noticed a distinct lag when snapping the throttle off idle, about half a second, after a few snaps the rroblem stopped being as obvious until left for another ten seconds or so. Now, the 90 has felt a bit slow on the get up compared to my 91, which is actually the worser of the two cars and after noticing this hesitation issue, I'm wondering if I'm dealing with an aged/faulty part. Both cars are completely standard and have no aftermarket parts fitted.

I'm just wondering what sort of things cause this hesitation off idle, the sluggishness I can leave to see if fixing the stutter fixes that too. I have read that a crook AFM can have an effect, though I haven't got the 91 at the moment to try part switching.

All advice welcome and I'll answer any questions as soon as I can.

no rotors

23rd June 2015, 18:50

FlavouredMilk

23rd June 2015, 18:58

gtxhawaii

23rd June 2015, 20:28

NGKs have a better rep than the original black OEM wires. If the car runs smooth but hesitates, you may have to look further. Let the injector cleaner work? Inspect for vacuum leaks by douching everywhere with WD40. When the idle changes any, you just wetted out a leak.
All the old gas run out of the tank and lines yet?
Any engine driveability issue calls for cleaning and resecuring all electrical grounds. And checking for stored CEL codes using a paper clip and the directions in Garage. Link to Garage at the bottom of every page here.
If you are familiar with doing a Safe water drip cylinder cleaning through a vacuum port in the intake, it may improve power and driveability. Done wrong you can hydrolock the engine and bend rods.
Check AFM settings and the Throttle Body contact adjustment. That and ignition timing are about all a Miata has you can 'tune'. All matter.
Open the air filter box to look for varmint homes and damage. This happens. Oz has snakes we don't have to be careful of discovering, nor do we have Funnel Webs and other unpleasant spiders, Work aware? The stock paper panel air cleaner is superb, all but impossible to improve for flow and filters dirt better than alternatives. It has to be too dirty to even touch barehanded before flow actually tests as impaired. Foam substitutes are poor alternatives.

Many local parts stores about Oz should have the NGK Blues, several Fords with Mazda engines use them. The coil end boots are not always glued on correctly and can prevent wire ends staying properly set. I break the glued on boots free and slide them back. Then feel and see the end bottom in the coil. Finally folding the boot back in place.
To fit the plug boots in place, you have to be the more determined part of the equation. 'Burping' any trapped air may help.

Oil in a plug well means the valve cover gasket is leaking, the oil will damage the plug boot and let the current short around the plug. Mazda valve cover gaskets work better than other brands. Inspect the heater hose for oiling as well. Both the gasket and the CAS O-ring can fail and oil the hose. If so, it will soften and swell, eventually failing at a bad time, maybe the most common reason for Mazda head gasket work or engine replacement.
If the temp gauge is at H or approaching, you many Have damage or at best seconds to shut it down and coast to a stop. Not locking the steering wheel when turning off the motor is the better alternative if in motion.