Sluggish 535iA

[nealf]

Hi my '90 feels a bit sluggish (150,000) and the gas mileage sucks (ave 14.8). What can I do to tune it up? It has been quite a while since adjusting the valves, plugs, etc.

[Alexlind123]

I think a general tune-up usually includes new plugs, cap and rotor and plug wires. The O2 sensor might be the culprit as well.

[Jeff N.]

Try the stop test and see if you get any codes. O2 Sensor's a good suggestion. 14.8 with city driving and oxygenated fuel is not unreasonable mileage to see.

[genphreak]

Try the stop test and see if you get any codes. O2 Sensor's a good suggestion. 14.8 with city driving and oxygenated fuel is not unreasonable mileage to see. In order of importance;

1. Stomp test (if your car does it)- depends on the market its sold in (it is a Californian regulation if not a US one that cars did this- euro ones don't).
2. Check for air leaks in the any of the intake boots, dipstick seals, block gaskets, vacuum pipes and intake manifold. May be a good time to do a valve adjustment and replace the valve cover gasket (to be double sure you can carefully clean and seal both sides with hylomar (be sure to tighten the nuts only to the right torque)
3. ICV for smooth operation and correct resistance
4. Spark plug firing and condition
5. O2 sensor (does not come up in the codes until (often) too late)
6. AFM if nothing else works (don't leave the O2 sensor they are only $100 and need to be changed more regularly than they ever are).
7. Fuel injectors- remove and test (check spark plug condition)
8. Catalytics, brakes, tranny, wheel alignment (could eb a combination)
9. Now I'm scraping the barrel here...

To fix sluggishness if the above do not- change tranny fluid to Castrol Transmax Z (synthetic) after a good flush (ie prior change) with Dexron II or III and a new filter each time. And buy an EAT chip- that helps fix a lot!

Synthetic in the tranny will help it go longer and may help to smoothen your changes and get more consistent operation.

However the economy sounds normal. I get slightly worse economy with a (suspected) bad AFM and new everything else (on standard unleaded).

btw; If it starts running badly do not leave it, the cat will die and cause more trouble (this takes time though) and you'll burn too much fuel and pollute your oil more quickly with combustion by-products too. Its very easy to check all this stuff if you have a Bently manual ($52).