ok I have almost gotten fed up with this truck (87 k5 blazer 350 TBI 5.7)and am about ready to scrap it and take my losses. I finally got the truck running and timed. now we're back to where I started when I bought the truck. you can see everything I have replaced in the below list.
but I'm getting ready to replace all the vacuum lines in the truck and priced the parts at the local auto parts store.
what it's doing is ...
when driving it bogs down like its getting too much fuel or too much air and the map sensor goes hay wire. it is idled way to low, at idle it wants to die. but keeping my foot on the gas slightly keeps her running. I have noticed that some of the boots on the vacuum lines are warn and was wondering what size I need to replace it or could I just use a hose without buying the plastic hose then buying the fittings for it. there are 3 hoses in the front of the TBI one is to the PCV valve. one is for the charcoal canister. one splits off to the EGR Vacuum Solenoid, and one split to the air purge valve. on the back the map sensor is hooked up to that. could i replace the hoses with flex hose all one size e.g.: 1/4 in. hose from port to port on all of them as long as i use hose clamps or do i have to build new Vac. lines like the ones I'm using 5/32 with 1/4 in ends.
map sensor... new
EGR valve ... new
TBI gaskets complete rebuild ... almost new
fuel pump and floater gauge... new
idle air control... new
intake manifold... used but cleaned replaced
intake manifold gaskets ... new
spark plugs... new
wires... new
dizzy cap.... new
ignition control module .... new
thermostat... new
fuel filter... new
injectors x2 .... new
fuel pressure regulator (TBI).... new
oil change and filter.... new
o2 sensor.... new
tested the Throttle sensor.... working
coolant sensor.... new

 

Just use regular rubber vacuum hose. Advance sells T's and plastic jump fittings to go from one size to another (my local napa doesn't carry them).

Your problem sounds like timing is retarded. Have you set timing with est bypass wire unplugged?

 

I've got the same problem with mine. I replaced the TPS, TBI, and map sensor vac line so far as well as all new gaskets. I'm wondering what could be causing this. Mine lopes at idle and then when you step on it it tries to die like its getting too much fuel or too much air. I don't know what's wrong either.

 

Oh and mine is an 89 K5 Blazer with the 5.7l TBI.

 

I unplugged the est. wire and turned the dizzy counter clock wise to above 8 deg tdc and it seemed to idle better but I could not see the timing mark I'm going to try to pull the dizzy out this week end and turn the engine one rotation to see if its comp stroke or exhaust stroke. its weird today it ran great but it was warm except the idle.

 

My money is still on the timing. Why couldn't you see the timing mark? You painted it with whiteout, right? The engine will run with EST unplugged from about 15* retarded to 40* advanced, and 40* is a long way before the timing tab above the harmonic balancer.

Have you guys checked your CTS (coolant temp sensor, top front of intake, 2 wire plug)? While you're there, clean the sensor ground (use sand paper on the intake and the ring terminal). Faulty measurements will cause incorrect fueling and can have a slight impact on timing, too.

approximate resistance specifications:
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

 

thanks for that info I'm going to check it tomorrow. I was wondering if anyone knows where a diverter valve cross reference list is so I can take one to the junk yard and get the right one. I have been looking around and can't find one anywhere that fits and I really don't want to buy a new one @ 250$ and it not be it. I remove the hose from the valve and the engine idles where its supposed to but plug the hose back in and it wants to die again. the one at auto zone is part number DV94.

 

the mark was off of the timing mark i can see it easly w/ the light. but it was firing on #2 when i hooked it up it was tdc #2 when the mark was not able to be seen so i put it back on # 1 and checked the timing she is running good now but still low idle i think it might be the air controll valve its not pumping air out of the valve so im going to the junk yard to pull some off today or tomarrow to test them i found the list i needed for the oem DV85, 17087137. at http://www.oreillyauto.com/site/c/de...2124&ppt=C0018

 

What condition is the harmonic balancer in? There is a rubber I guess you'd call it a gasket between the inner hub and the outer ring. Those can go bad over time and the outer ring will move a little and make it so your timing readings are off.