follow up to stalling Topaz

I'm getting multiple fault codes from an 89 topaz (2.3 with airconditioning) Here are the codes:

13 RPM idle out of range/low: cant control idle vachum leak,TB base idle off,idle air valve dirty or bad, EGR stuck open idle out of spec same as code 12

31 EVP or PFE circuit below minimum voltage Bad EVP/PFE sensor, no exhaust backpressure (really doesn't really cause problems) or inopperative EGR

42 HEGO (HO2S) sendor voltage high / system rich Bad O2, bad MAP sensor, Bad fuel regulator, Leaking injectors, restriction in fuel return line, clogged exhaust lowering vachum

70 ECM failure Data communication link error, bad ECM

73 Insuficiant throttle position change No change in TPS signal, no dynamic response sets this.

95 Fuel pump secondary circuit fault Fuel pump monitor has seen a fault in the fuel pumps or circuit

I'm wondering if I really have all these problems or if I just have three problems. Assuming I don't have a vacuum leak somewhere (I'll test that) I'm wondering if a bad MAP or O2 sensor could cause the ECM code?

Could anything other than a problem with the fuel pump cause the code 95?

How do you test an EGR valve?

And what exactly is a EVP or PFE sensor? I can't find a definition anywhere.

Thanks in advance.

Paul.

It's a very simple device, operated by vacuum. Apply a handheld vacuum pump to it and check that it doesn't leak. If you remove it, you can actually see the valve opening when you do that. On the vehicle, fully opening the valve will dramatically affect idle, probably causing the engine to stall. If you don't have a vacuum pump, you could probably find an unused port on the vacuum manifold and briefly hook to it, or put a T into another vacuum line (just make sure not to cause a big leak in the process). If there is no response from applying vacuum to the valve, the passageways are clogged, or the valve doesn't work. The former is much more likely, as the older EGR systems were prone to carbon deposits. If your 89 Topaz has never had the EGR system serviced, you can bet that it's badly clogged. Take the valve off, and do your best to clean the mess. You may need to remove the adapter as well (which probably requires removing the throttle body). If you see a lot of carbon, the valve itself will most likely be clogged too, and unable to fully close (if really bad, this may be causing your code 13 ). With a lot of patience and a handheld vacuum pump you can hold it open and scrape inside. That's what I used to do. Or simply get a new one - probably around $30 in auto stores.

The EGR valve operates in closed-loop mode. This means that there is a mechanism which senses what it's doing. Essentially, there are two ways: position (EVP) or flow/pressure sensing (PFE, later changed to DPFE). EVP is a potentiometer that simply measures how far the valve opened. If you have it, you'll notice a small plastic cylinder (about 1" in diameter) on top of the valve, with a 3-wire electrical connector. They rarely fail, but everything is possible... Check that the connector is intact and the contacts not corroded. If you have PFE, there will be a thin tube attached somewhere along to the EGR flow path, leading to a sensor, possibly mounted on the firewall. No experience with PFE, but its newer brother, the DPFE is prone to failure (electronics and hot corrosive gasses don't mix too well). Your code 31 may be due to a bad PFE, if your vehicle is equipped with one.

Hope this helps a bit.