I have spent the last few days reading on this forum and have gotten a lot of ideas for things to check and for that I want to say thanks for all the informative posts. I was glad to have stumbled upon this site.

I am still checking and replacing things but was hoping maybe somebody may recognise my problem and save me some time and money so here goes.

I have a 1995 Aerostar, 4.0, 4wd, Canadian model,121000 mi., bought it used about a year ago with 92000 mi untill now have only replaced the breaks. A while ago I noticed it would miss occasionaly while idleing at a stop light. I put some injector cleaner in it and it seemed shortly after that it started to surge while accelerating or when going up hills. Also it did not want to start when hot. I put a second dose of cleaner in it and it now will start when hot but sometimes I have to push on the gas pedal.

It has continued to get worse to the point that now the surge is very severe and it will on occasion almost die/stall when accelerating hard and make a loud thunk like something has locked up. The thunk is so severe that it shakes the entire vehicle!

What seemed to have started as a small problem has become very severe. It now idles fine at stop lights and runs smoothly while on the freeway at constant speeds. It seems to only occur under a load like pulling a hill or accelerating from a stop and increases in severety when the A/C is on.

I have gone from suspecting the transmission to the 4wd system to vaccuum leak to fuel pump/system to TPS. So far I have replaced the spark plugs(one of which was incorrect)air filter, oil and filter, checked tranny fluid, checked vaccuum lines(visual)checked u-joints,replaced fuel filter.I am going out to replace the plug wires shortly.

Sorry, this is so long, just trying to provide as much info as possible. Any ideas will be greatly appreciated.

 

I had a similar situation with my 95. It would surge, usually under heavy load, and was a bit reluctant on downshifts. It never did set a code. I removed and cleaned the MAF sensor and it seemed to fix the problem.

If it is using a little bit of oil, usually around a quart between changes, check the intake manifold bolts. Be warned, they are not easy to get to. Hope this helps.

 

Thanks tbpbft,

It uses very little oil between changes if any. While I was changing plug wires it did remove and clean the MAF and neither of those seemed to help.
Thanks for the suggestions but unfortunately I will have to keeep looking.

One thing that makes me think it may be a vaccuum leak is that when under a very heavy load with the A/C on the vent will change from the dashboard to the defrost and then back again when I let of the accelerator? What do you make of that?

 

Check the fuel pump pressure on first.
When clean MAF sensor you must disconnect the storage cell at least 5 minutes to erase previous codes.

 

1990 4.0 o2 sensor?

 

Clean the IAB valve on the TB and clean the TB itself. Fords are notorious for this problem. Also, a TPS going bad can cause this problem.

 

I had the same problem last week, Remove the hose from the top of the egr valve and plug it up, see if this works. My is now smooth as silk,

 

I had similar problem with my 92 4.0 litre Aerostar with 250.000 km. It was hesitating when starting out from a stop and bucking during small load changes at highway speeds. I changed the spark plugs and wires and cleaned the MAF (not too dirty) and it seems to run fine now. It also idles rough sometimes and injector cleaner usually clears it up.