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Hey everyone. Still working on my uncle’s ’99 Mazda B2500. So, the problem is a very rough idle/stalling problem. Thing is, if you let it sit to cool down for a while, then start it and don’t touch the throttle, it idles fine. Second you snap the throttle or anything, it runs very rough below about 1500 RPM and will almost guaranteed stall after a second or two. Keep it above 1500 RPM, and she runs fine. I replaced what I thought was a bad IAC valve, but that didn’t solve it. Any ideas? I was thinking either the TPS or the EGR valve / DPFE sensor.
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Any codes?
Last time the air cleaner, plugs and wires(if equipped with wires), fuel filter (if equipped) were replaced?
May be a fuel delivery issue…. Best to check fuel pressure while running and what the pressure is like when the vehicle is turned off to see if the pressure holds (issues with fuel injectors)
-Karl
No codes. Air filter is nearly brand new. Plug and wires I’m not sure, but I can check. Fuel filter I’m not sure, but I can check also. I believe I have a fuel gauge. I’ll just need a T-connector so I can get a running pressure check vs just a straight line for a static check. I think I’ll do a quick and dirty on the EGR and see if it can hold a vacuum. Afterwards, I’ll see if depressing the EGR stalls the engine like it should. Any ideas on how to diagnose a bad TPS besides erratic voltage on the signal wire during a sweep test with a DMM? Naturally I’ll ensure power and ground is good. I wish I had a 2 channel scope, it’d make my life much easier for diagnosing…
First and foremost, I don’t know why I put this as a 1992 Mazda B2500, it’s a 1999.
Secondly, I believe I found the problem. I was checking the TPS and EGR today. The TPS passed the sweep test with my DMM. Nice smooth increase, peaked around 4.5 or 4.7 max throttle. I moved on to the EGR system. The kind of EGR on this vehicle does not have an exposed diaphragm, so I couldn’t quick and dirty it from there. I went to the EGR Vacuum Regulator Solenoid (EVR Solenoid) and took the cap off. I plugged it with my finger and the engine started falling on its face as it should. At the same time, I was T-pinned into the DPFE sensor signal wire and it definitely didn’t respond correctly. KOEO it sits at like 1.4V, running about the same. While it was running, when I plugged the EVR solenoid port it would drop to like .80V, and bounce between .80V and 1.4V or so. From what I understand, it should be going upwards of 4V. What do you guys think? A little digging and I’ve seen that a failing DPFE will create a lean condition and stuttering/stalling, which is what I have.
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