I have a 92 Ranger with 175000 miles and it went from running beautifully to having no power and stumbling, no check engine light came on and no codes for key on engine off and no continuous memory codes. I replaced the fuel filter and fuel pump and it ran great and I was smiling until the next morning and it did the same thing. I had just recently pulled the upper intake manifold and cleaned out the EGR valve port, cleaned the EGR valve as well as the air idle valve. It did have an idle problem when I was done and the problem with that was something I've done before by reversing the vacuum lines on the EGR solenoid. I waited for it to warm up outside before trouble shooting it, I started it and while it was stumbling I applied a vacuum to the EGR valve and the engine didn't stall. I started to remove the EGR valve but decided not to started it and it ran fine again and has since. I'm afraid I'll be in traffic and this will happen again can someone explain to me how to do the wiggle test.

 

EGR(exhaust gas recirculation) system is pretty simple

Computer has a vacuum solenoid it controls that passes intake vacuum to EGR valve to open it, computer Pulses the power to open solenoid a little or alot, it has very precise control.
There is often a sensor on the valve or a pressure sensor on EGR exhaust tube to tell computer if valve is opening and how much it is opening.

EGR system is only used after engine warms up, and then only when engine is under a load.
EGR system reduces heat build up in the cylinders when engine is running a Rich mix, i.e. accelerating or climbing a hill or hauling a load
Rich mix burns hotter and that spikes NOX emissions, a deadly toxic gas, adding exhaust gases to the "air" in the intake at that time reduces the temperature in the cylinders so reduces NOX emissions.
Yes, adding HOT exhaust reduces temp, lol, ain't Physics great
Bonus side effect is that spark advance can be reduced for better power without the worry of pinging/knocking when running Regular(87 octane) gasoline
Pinging/knocking comes from pre-ignition, lower octane fuel is self igniting in HOT cylinder


Your idling engine should start to stall if you open EGR Valve by applying vacuum to it.
So something is wrong there.

Yes, EGR Valve opening too much or at the wrong time will cause loss of power and stumbling

 

I think you have that backwards the exhaust gas is allowed to recirculate because of a lean condition which causes the engine to run hot, the exhaust gas recirculates lowering the oxygen in the intake and enriching the mixture causing it to run cooler and reducing NOx and your right exhaust gas will not circulate with a cold engine nor at idle. I want to be able to reproduce the cause of this stumbling engine, it was stumbling just like if the EGR valve were opening at idle, and if it were I would get a trouble code from my EGR valve position sensor. I thought about a failing MAF sensor maybe a bad ignition switch it's been running fine but I'm the type of person that has to know why it was running like it was because there is a chance it will do that again.

 

Well the actual physics of it are a little different, rich mix does make for cooler running, and lean mix hotter, but only in general terms.
When you add engine load it changes a bit, in this case computer adds richer mix to gain more power, and a richer mix burns faster and hotter(releases more energy), the inert(already burned) exhaust gases slow down the flame front so lower the higher temperature spike, engine still heats up, i.e. temp gauge when climbing a long grade will go up a bit.
If it was just a matter of lean or rich computer could just adjust fuel flow and wouldn't need EGR system for that, engine needs the rich mix for more power, but it needs the inert gases added to slow down the burn rate to lower NOX levels.
At Wide Open throttle(WOT) neither the EGR or the O2 sensors are used so engine can get maximum power.


EGR solenoid is operated by the computer Grounding it, computer Pulses the Ground to vary the vacuum flowing to EGR Valve.
So EGR solenoid should get 12volts on 1 wire when key is on, other wire goes to computer, it is the control wire, the ground.
(IAC Valve works exactly the same way)

Now IF(big if), that Ground control wire had a bare spot and it touched any grounded metal part..............., then you have EGR solenoid activating intermittently
I would expect this to set a code for EGR Flow high

 

When this first happened the day before Thanksgiving I was jamming down the frw running great and then I had no power and engine stumbled just like a fuel problem but no trouble codes and then after changing fuel pump it ran great that day but the next morning when it was very cold out and engine was cold it started but same stumble, I ruled out the IAC because the first time this happened the IAC couldn't of had any effect on the engine. I think I'm going to start purposely causing faults and checking that trouble codes are being generated. I did a KOER yesterday and I get the engine id flashes but it never gives me the signal to goose the engine, I did it twice with no signal to goose the engine.