Hello once again ford fans,

I have an 87 f150 with a 5.0L. When I bought it a few months ago it had an idle problem. I cleaned the throttle body and intake, put in new plugs, wires, air filter, checked most of the sensors, plugged in the power steering switch, fixed some vaccuum leaks, checked the timing, fuel pressure(the booster pump seems noisy but the pressure always stays at 39 PSI). The truck idles great now except.......

While driving down the highway it feels as though you are hitting gusts of wind when you are not. I cannot maintain speed. When the truck is parked and I hold the throttle at specific rpms the engine will rev up hold and then drop 300-400 rpm and then return back up .It will do this consistantly. I have done this with the fuel press guage attached the the fuel pressure holds steady at 39 PSI. I am just about ready to give up on it and learn to live with it, expect that the fuel consumption seems higher than it should be.

Any ideas?

On another note the truck has dual tanks an the gauge doesn't work properly for either tank. When the tanks are full the guage stays above full for probably half of the tank and then starts droppping fast. I am assuming to much resistance or not enough which ever war ford works, but I am not sure where to start checking.

For the second time this yearI bought a vehicle that has a very strange problem and my hair is starting to turn grey and fall out.



I appreciate any advice
Cheers,
JB

 

Try disconnecting the vacuum hose to the egr valve and go for a test drive. It will turn the check engine light on, but don't worry about it - the light will go off after you hook the hose back up.

If the problem quits, there is something wrong with the EGR valve or the EGR valve sensor or controller.

My truck surges at cruise rpm's but goes away when I disconnect the EGR. I haven't got around to fixing it yet though - my RPM only drops slightly but I can still feel it. hopefully I'll fix it in a week or two.

If your problem persists even with the hose disconnected - i'm not sure where to go from there.

good luck

Carl

 

Disconnecting the EGR seemed to work. I put a vaccuum gauge on it and when ever there was vaccuum the rpm would drop significantly.

So my biggest problem was once again myself, over analyzing the situation.

Thanks
JB

 

Well, maybe you've found the problem but the EGR should make it idle weird, you're opening the valve when you apply vacuum. Why have you not pulled the codes?
http://www.off-road.com/ford/bigbroncos/tech/eec/index.html

I hope you've found your problem already, but the TPS could also create the symptoms you describe.

 

I have a code reader and I read the codes out of the truck, the only code I got was a code for the power steering switch which I fixed previously.

I had the vaccuum gauge teed into the egr signal. When I held the throttle in one place for a time, as soon there was vaccuum to open the egr the rpm would drop 300-400 rpm. When I disconect the egr and plug the vaccuum line the truck runs perfect. I drove it to work today (60 miles round trip) it drove better than it ever as.

During previous testing I disconnected the idle air control valve, MAP sensor, and TPS (at different times of course) and the problem exsisted in all cases. I didn't try the EGR before because I didn't realize that it could cause such a problem. The egr valve closes properly with out vaccuum so I think that is why it did not effect the idle.I don't really know what the problem is with EGR valve. I read some postings today related EGR problems and apparently it is a common point of failure, causing all sorts of symptoms.

Thanks,
JB