89 Chevy Silverado issues.

Yep, holding vacuum on the booster is a good thing. You can usually get about three good pumps of the brake pedal feeling the assist of vacuum. The green connector is map it’s a speed density motor, that’s an important sensor I believe you mentioned replaced. Yes, the iac seat can wear. I don’t remember the exact procedure but there is a way to ground it out from the aldl closing the pintle all the way with key on then unplugging it,then key off, unground aldl then start back up. Definitely get the exact procedure before poking around like that though. You might find it under base idle speed or setting idle speed. I’m thinking you got it narrowed down to leaky injectors if spark timing isn’t moving around. The knock sensor shouldn’t effect idle speed and those egr’s Can be a fickle pr!?k. Even faulty new ones sticking. I have my egr unplugged right now.sticky lifters piss off my knock sensors just off idle,computer retards timing and opens egr. Runs like crap first 1/8 throttle in closed loop. Ran great cold.

have not replaced MAP sensor,. I will test it tommorow, , it looks like it tests like the tps, reference volts, signal volts and ground, with a vacuum on it.

what I might try tommorow is dig out my timing light and see if the timing indicator is moving around, with the surge, this might tell me if the ecm is retarding the timing or not. if the ignition is holding fairly steady, then im thinking it should be a fuel delivery or mapping problem ?

I will check the injector spray pattern while I have the timing light out, too.
once this truck is right it should be good for a long TIME, because almost everything is getting checked , cleaned, tested or replaced.

I used to cut a beer can apart and make a block off for the egr. just completely seal the hole under the egr valve. better top end and no notice in loss of gas mileage. its nothing but a power robbing component that has potential to cause ALOT of problems., as u said many are crap right out of the box. I doubt the engine reburns anything out of the exhaust gas anyway, just a prop car manufacturers used to try and appease the govt pollution committees. I took the belt off my smog pump too and put it behind the seat until inspection time, ha

another way to reset the IAC is drive the truck over 40 mph for 5 min, when I reset mine, I had the back jacked up to do the brakes, so I just put it in gear and watched the speedometer go to around 42 mph, and ran it like that for a while. Feels odd sitting in the truck watching the speedo go to 42 mph while u just sit there going nowhere ha

You’ll get it,wether or not it likes it. The ecm uses the map to control fuel and timing so a steady signal is what you want at idle. I mentioned the iac procedure because it closes the pintle and remains closed while you check and set base idle,but in this case just to narrow down what was moving around. Keep at it,I’m excited to see what you find.

ive been researching the actron 9690 scanner, being Im going to have these trucks a while, I may get one. Alot of people are seeing that these old trucks werent all that bad, and dont want to pay 60,000 for a new truck, with a 4 cylinder twin turbo engine and aluminum body. these trucks will be like the c10s, everybody is trying to own one. yes, sooner or later the root issue will reveal itself, I may have another map sensor I can try in the shed. when I get back from the doctor today, the first thing im going to do is hook the timing light up, and see if the timing is being retarded or advance while idleing.. I wouldnt thin it should be moving much or at all at idle if nothing is amiss with the ignition system? if that is the case, then the side of my brain that keeps wanting to wander over to an ignition problem, can stop haunting me. ha I will then check the MAP i have a vacuum gauge and saw a chart that shows inches of vacuum and the corresponding voltage the MAP should be sending thru the signal wire to the computer, the reference voltage is the same as the tps, 5 vdc.

Somehow I missed a couple of your messages. The way you described the surging even when cold would make that map sensor much more suspect. I think you’ll see that signal moving around. Look very closely at the vacuume line,it may be collapsing on you or some crap in it. Use vacuum rated line on it only.

you know come to think of it, when we got the engine put all back together, we didnt even realize the map sensor was missing, we knew there was a plug connector not hooked up, but we were curious to see if it would run. we started it and it Idled great. It wasnt until we went to the junkyard, figured out what was missing and eventually put the map sensor and whatever else is on that bracket on. it seems like the idling problems then started. I also didnt realize the vacuum line from the back of the TBI wasnt hooked up, it wasnt even there. yet the truck idled fine, with that vacuum leak and no MAP sensor.
Im thinking that some of the vacuum circuits in the TBI Are critical to vacuum pressure and some are not,. take the pcv valve, it sucks in an enormous amount of air. I cannot see where this would be calculated into the engine management control. it is almost an open vacuum stream. why the engine idled great with the map sensor missing and a huge vacuum leak at the back of the tbi is strange.
it also had the missing o2 sensor in the manifold at that time.
Maybe it all balanced out somehow.
"" ya know what I think we should do Norton? whats dat Ralph? i tink we should remove dat o2 sensa.."" lol

Im going to check the vacuum line, i THINK TODAY may be the day we figure it out. It would be just my luck to have gotten a MAP out of the junkyard and its bad.
would a scanner that reads OBD1 have seen this from the beginning? would it show the map voltage hopping around? or just quickly fluctuating fuel trims.?

The otc genisys shows map it’s a real important sensor in non maf motors. You need to keep that o2 sensor in the manifold. It doesn’t start working till around 600°f ,zirconia type I think. It won’t really come into play at idle,but Anywhere down stream will just give you poor performance and mpg and probably that code 43 or whatever o2 code applies. The computer will substitute the non essential inputs using a base fuel map,you still had coolant temp and tps at the time map was missing, probably sucked off idle though. I’m not intimately familiar with actron but as long as it has the 12pin gm obd1 connector it’ll tell you something. They weren’t standardized then meaning not all scan tools gave the same info. I was a little surprised how much more info I got out of the otc on my 93’ compared to a friends older little hand held. I’m guessing archeologists in a couple hundred years are gonna wonder what that little black box with rubber hose is with a 45cal hole through it.

That actron 9690 doesn’t look to bad for about $250 on flebay. The only thing you would be missing is the bidirectional to manually actuate things from the tool, but you can certainly get by without it.

I checked the timing with the engine running, the pointer is moving back and forth abt 1/2 inch. I tested the MAP, the signal voltage is all over the place, fluctuating from 0.88 vdc to 2.55 vdc. its fluctuating so fast, you can hardly read the numbers. it has the 5 volt refrence on the other wire, and a good path to ground on the remaining wire. I removed the map sensor to get a good look at it. the backside looks like it has melted sone in the corner. I dont know if this is from an internal problem or if it was heat from the outside near the engine. it sits on a bracket well off of the engine.. im thinking the MAp is the culprit. I would think that the timing moving around is due to the map being bad and the ignition module is just doing what its signaled to do when the map signals it.
Im going to get a new sensor tommorow and see if that fixes it. the sensor should not have a hot melt spot on it, and I dont think the voltage should be fluctuating that fast or that much. probably 5 different values a second. like a confused calculator.

im afraid to swap parts off my other truck because of experiences ive had in my life. heres one example.. I pulled and cleaned A tough old german ladys window A/C. she kept telling me she was worried abt the water.. ad nausium,. finally we got the A/C back into the window, and the exact moment I plugged the A/C in, everything in the house went out.., She started screaming, you ruined my electric, you ruined my vires, you ruined my house!!!! So I went to the breaker box, and nothing was tripped. went in the backyard, to see if meter was running, nothing. so I went in the front to go see if her neighbor had power, when I spotted the big TU Electric truck. they had cut the power to change a transformer.
so I dont want to mess with my other truck and something fail, just as I happened to pull it off, then im out there really sweating it, because that is my fishing truck.

im going to read the online manual for the 9690 and see what all it does. I think in maybe a year or 2 I will have learned enough to be able to use it with good results. im still learning how fuel trims work, and emissions but the big picture is starting to form. Ive learned alot watching danners vids, and a guy called southwest main auto repair, dans brother, and eric the car guy, and yourself, and im appreciative.
If I could find a vid on how exactly the gm computer sequence of operation works, I would get alot out of it. I understand the gm bypass ignition system, its the fuel mapping I would like to know intimately. like what EXACTLY is happening when its surging, is the map reference sensor out of tolerance and the computers sees this and tries to default the fuel trims back to a preset parameter or does it just ingore the errant signal and depend on the coolant temp sensor, and or tps signal.. basically what is going on in the ecm.

Congratulations, I knew you’d find it. I know exactly what you mean on the Murphy’s law and apparently the old German lady did too. I’d also have to pass any thanks on to Paul as well. On the fuel mapping and what the ecm is thinking start at MOATES.NET and poke around and then EFI LIVE. I think you’ll find them interesting.
Also, I’m not positive, but I think the voltage swing max to min should only be about 1.5v on these map’s. If you had something like a mityvac hand pump to apply a steady 19 or 20” of vac, you could remove the variable of fluctuating engine vac. For future reference.

will get a map sensor probably tommorow and pray that fixes it,, the way the signal was jumping gives me great confidence that the map is bad. what is the square black box with the 5 pin connector that mounts right next to the map sensor. it doesnt have anything but a connector plug, no vacuum.

yes I appreciate everyone who contributed. Im going to really enjoy not hearing the truck surge,. Im still teaching my son how to drive standard, so if it is running good, it will be easier. we bought it for 600 and probably put abt 800 in parts in it. probably 60 hours of labor. Im going to give my son the option to buy me out, if he doesnt want it, we will sell it. I hope he keeps it, we spent alot of hours together working on it, and he learned alot. if we do sell it somebodys going to get a good rust free truck, with a lot of new parts. everything works. the only downside is it has no a/c system. were going to put new tires on it soon. the tires will pass inspection but they are worn. headliner is gone. seat is worn, windshield has a chip.. abt
what would be expected for an old truck.
we have replaced battery, ignition switch, radiator, water pump, belt , pulleys, fan, hoses , t stat, brakes and hardware, differential fluid, topped of transfer case fluid, replaced worn sway arm bushings in front, had heads decked and valves worked, complete top end gasket set, new o2 sensor, new tps sensor coming, new cap and rotor, ingnition module replaced and distributor refubished, fuel filter removed and cleaned. new washable air filter. the only thing it needs left to pass inspection is the exhaust pipe needs to be extended to the outside of the bumper. all 4 headlights and tailight lenses were replaced before we got the truck. wish he had replaced the casette player,, haha

He should definitely keep it,a spare vehicle or just don’t want to take that fourth friend with you. His toys are gonna get bigger and need to get them home. That little square 5pin box should be the knock sensor module. I can’t remember exactly what they call it. It sends its info to the computer to aid in the spark timing.

did some research and the map does control fuel and spark, so I see why the ignition is moving around. would also explain the occasional backfire. the engine is a confused mess..... signal jumping around, idle jumping around. if the map controls timing and fuel, I wonder how it interacts with the TPS. THE TPS is also sending a signal voltage to the ECM. Im thinking that once engine is off idle the tps may take over the fuel parameters and the MAP sends signal to the ecm to advance timing thru ignition module.. just a guess. but they both cant be controlling fuel and timing> these years dont have crank or camshaft ref sensors.