1986 volvo 740 bad on gas! Help

[richyrich514]

Trying to iron out a few kinks after acquiring this beauty.

1986 740 wagon - non turbo
190 000km
Automatic

Ive been keeping track of my gas mileage and a full tank is getting me approx 350km! Give or take

From what i read i should be getting close to 525 or so of mixed driving.

So far
I have cleaned out the flame trap
The IAC
(Both were not bad at all to begin with)

Previous owner claims he has changed the wires, plugs, rotor , cap)

My idle has been a bit weird as of today
With it in park i rev her up to 3000 and then it with drop to 1100 and sometimes stay there.. Other times it will drop to the normal 800-900 after a few moments

On cold starts if i start her up and drive her off after a minute of warming up she seems like shes either getting too much gas or not enough and is at a loss of power for a 100feet. But only for the first pull after 100 feet on a cold start.

I bought a coolant temp sensor today
But i was thinking it might be the TPS..?
I will clean the throttle body tomorrow when the gasket gets to the parts store.
Maybe the knock sensor?


Any input would be appreciated!

Thanks

[rogerthechorister]

Here is the UK we talk of miles per gallon. If you rephrase your statistics in comparable terms you may get some relevant answers.

[richyrich514]

Originally Posted by rogerthechorister

Here is the UK we talk of miles per gallon. If you rephrase your statistics in comparable terms you may get some relevant answers.

I am basically looking for help concerning the symptoms i mentioned and that i am not getting the proper amount of miles per tank.

[rogerthechorister]

So, measure YOUR tank size and do the arithmetic. I'd expect a 740 Estate of that age, petrol, normally aspirated, to do about 25 mpg, people with lighter right feet might get nearer to 30 mpg.

Once you have done that it will give us SOMEWHERE to start, since we are not mindreaders

[richyrich514]

I should be getting 20-25 mpg, i have 15 gallon tank, more or less. This is 300-375 miles, 500+kms. So, yeah, the mileage is bad.

[Prufrock]

Apart from the poor fuel consumption you report, does the car run ok ?

You say previous owner changed plugs - when, are they the correct heat range, have you checked the colour (running rich = sooty plugs) ?

You say mixed driving, the official (Volvo) urban figure for this car is a very optimistic 24.6 mpg - my own 1986 745 auto probably gets around 18-20 mpg on short local runs (which is the nearest I get to urban as I live in a rural area).

I can get near 40 mpg on a steady motorway type run, but these cars take some experience to get the best out of them: on a run the sweet spot is around 55-60 mpg, any faster and the mpg drops radically. You need to learn to drive a 740 on light throttle opening and often, where conditions permit, a trailing throttle.

Is top gear, overdrive 4th, locking up (assuming you have the AW gearbox) ?

Jon
700/900 Register Keeper VOC.

[richyrich514]

Originally Posted by Prufrock

Apart from the poor fuel consumption you report, does the car run ok ?

You say previous owner changed plugs - when, are they the correct heat range, have you checked the colour (running rich = sooty plugs) ?

You say mixed driving, the official (Volvo) urban figure for this car is a very optimistic 24.6 mpg - my own 1986 745 auto probably gets around 18-20 mpg on short local runs (which is the nearest I get to urban as I live in a rural area).

I can get near 40 mpg on a steady motorway type run, but these cars take some experience to get the best out of them: on a run the sweet spot is around 55-60 mpg, any faster and the mpg drops radically. You need to learn to drive a 740 on light throttle opening and often, where conditions permit, a trailing throttle.

Is top gear, overdrive 4th, locking up (assuming you have the AW gearbox) ?

Jon
700/900 Register Keeper VOC.

I changed the engine temp sensor and the cleaned out the throttle body with the proper intake cleaner and she is running a lot
better now! I will check all the ignition parts this weekend to see what else is going on.

Thanks for the info

[richyrich514]

After a day it still has good power but the idle still drops a bit and oea back to normal when im at a red light. It doesnt do it all the time. Could it still be the tps?

[baggy798]

Have you adjusted the throttle body after you cleaned it? The TPS is just a simple switch that should click when you move the throttle plate ever so slightly off the 'stop' (about 0.2mm).

It won't affect fuel usage during normal running though.

[richyrich514]

I did not adjust it.. And the tps clicks pretty mich right when the fly opens... So weird how the idle was fixed and regained power after cleaning the theottle body. And a day later the idle is almost acting the same! Stays in high idle at times with it in neutral.. Like 1200-1300rpm and with it in drive at a red ligt the rpm keeps bouncing from 900 to 600..