Erratic rough running '95 GMC Vandura

[Steve C.]

My work van is a '95 G2500 Vandura with the 5.7 TBI - 174k.  I've suspected the EGR valve needed replaced for some time, as it would run good around town but after 15 or 20 miles on the highway it would start to stumble and  bog down a little.  Once I'd get back in town it would act fine. Check engine light came on before stumbling started.  I procrastinated replacing the EGR valve due to having to pull the doghouse.

 

Last week, after about 15 miles, it started stumbling again, but got much worse than before.  Felt like it was running on seven instead of eight.  When I got in to town driving, it continued to stumble, and idled erratically, going back and forth between smooth and very, very rough.  The next morning it started and ran fine, until it reached normal operating temp, when it started the rough idle and stumbling again.

 

I did the paper clip OBD1 test, and it showed code 32.  Pulled the doghouse, then the EGR, and sure enough the diaphragm was shot.  Replaced with a new valve, unhooked the battery cable to clear the codes, and all appeared well.  Until I drove it on the highway and got up to operating temp, and then the stumble came back, same as before.  It's not throwing any codes now.

 

I'd appreciate any suggestions.  I can't tell if it's fuel or fire, but it only happens once the temp gauge is up to normal.

 

 

[Mikebtte]

I would check fuel pressure as the issues is happening when fuel demand is high.

Could be pump or regulator not working but checking pressure is always a good start on a TBI. May try changing fuel filter if it has not been done in a while.

[Steve C.]

50 minutes ago, Mikebtte said:

I would check fuel pressure as the issues is happening when fuel demand is high.

Could be pump or regulator not working but checking pressure is always a good start on a TBI. May try changing fuel filter if it has not been done in a while.

When I bought the van five years and about 40,000 miles ago I had a new pump installed by a local shop, as It had been running weak.  That took care of that.  This is different.  It runs real strong, like it was new, for the first five or ten minutes every morning.  Once it starts to act up, it stumbles and misses even at low speeds here in town, even sitting at a stop light.  When it acts up (feels kind of like a dead miss, like a bad plug or wire, but if that were the case I don't know how it would run so strong first thing in the morning) on the highway, I can tromp it hard and it seems to partially, but not completely, snap out of it.

 

I've been wondering if there's an ignition module issue.  Do they ever fail this way?  I've had ignition modules die on other vehicles, but they usually just die.  This seems to be heat related.

 

[Mikebtte]

The temp sensor will cause a rich condition on start up and a lean condition warm. If the sensor is not reading that it is warm it will cause you to run rich and get a stumble. Worth ohming it out. No cost to check.

[Steve C.]

10 hours ago, Mikebtte said:

The temp sensor will cause a rich condition on start up and a lean condition warm. If the sensor is not reading that it is warm it will cause you to run rich and get a stumble. Worth ohming it out. No cost to check.

Makes sense - where is it and how to I check it?

 

I really appreciate your input.

Edited September 24, 2019 by Steve C.

[Mikebtte]

Should be on the front of the intake manifold

 

Coolant sensor approximate resistance specifications: Sourced VIA the internet
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C

[Steve C.]

Thanks Michael. I'll check it when I get a chance.

[riverbanks]

A guy had a similar problem a while ago,I think the replacement egr was the wrong one,it comes to mind,the hole size on the vacuum port,small ,I think is yours,online you get the common one,large?,is the egr the same?

[Steve C.]

Update: it's running better, but still doing some stumbling and some rough idling.  Not as bad as before, though.

 

Now it's throwing code 32 again. which is EGR or MAP sensor.  Since the stumbling has been occurring for some time, suddenly got worse last week, then improved but didn't go away after the EGR replacement, and I still get the same code, it makes sense to me that the MAP sensor is probably bad.  Especially after reading up on the symptoms of a bad MAP sensor.

 

I don't like to just throw parts at a problem, but this is a relatively cheap part and not that hard to change, so I'm leaning toward replacing it.

 

Does this make sense to you guys?

Edited September 27, 2019 by Steve C.

[Mikebtte]

I had an extra at one time for testing this. Wish I still did as I would send it to you to save the trouble.

[riverbanks]

32,to me ,means the map is good,it's just seeing a wide voltage reading,cause it can't control the egr,ayear ago?,on here, Mike or dave,gave the info on egr

[flyingfool]

friend has the same erradic idle, new tps sensor fixed the issue