I'm stumped 2.8L

[sourgrout]

I have a 1990 with a 2.8l TBI I have done a major tune up and cleaned the throttle body inside and out. The truck has a slight hesistation from a stop and when I'm cruising down the road around 25-35 mph it jerks and stumbles. When I block the egr by plugging the vacuum line it goes away and she runs perfect. So I replaced the egr and tested the egr selenoid valve and it still does it. Its like its getting too much egr at lower rpms. It idles great with or without the egr plugged and if I stomp on it it has plenty of get up and no hesitation. just acts up when driving lightly. Anyone else have this same thing happen to them? No trouble codes and all sensors have been
checked/adjusted (that I know of)
Thanks

[hardparts]

does it go away when you unplug the solenoid?
if it does then something is causing the solenoid to open.
if not then the solenoid is sticking open just a little.

[sourgrout]

Thats a great question, I did replace the selenoid but it still does it, however your right the computer may be activating the selenoid prematurely or too much. I'll try unpluging it tonight and see if that works.

[dmbrisket 51]

you may have a vaccume leake somewhere, bad 02 isn't likely the cause, but is possible does she every back fire at ya/miss consistently?

[sourgrout]

No she'll do a miss when I first start it kind of a light thump...thump thump... So far from what I've been able to find is some are saying it may be a weak spray pattern from the injectors but I'm hesitant because a set of injectors is close to 200 bucks, and it would really suck to replace em and find it still does it. The only thing i have going is: no codes, full tune up, good fuel pressure, and the MAP, IAC, TPS, O2, and ETC all seem to be in spec or atleast working (to some degree), timing is dead on, valves adjusted, new egr, and TBI cleaned up (inside and out). I also heard some say that old coolant can have a negative charge and effect sensors that come in contact with the coolant, one mechanic saying that even a -.25 voltage in the coolant will cause wierd things to happen to sensors... but that sounds far out. I dunno, I'm use to working on small block and big block chevy's with HEI and a tuned Q-jet, thesed computer jobs got me.

[dmbrisket 51]

if your sure it is not an 02, and its not the egr itselfe, time to check for a lean condition (vaccume leak) 2 ways of doin this, my way is to stick a small pin hole in the intake tube, and push the straw from a can of carb cleaner in there, and simotainuasly throttle it and give er a squrt from the can, if it chugs and doesn't like the cleaner, its not lean, if it runs good/better with the cleaner sprayed at a throttle snap, then you have a leak somewhere, do the next step to find the leak if it isn't audable, (some people jump right to this step and dont do the first) the other is to spray the carb cleaner at things with vaccume in them, and listen for a change in idel, if it changes, then the cleaner got in and there is your leak

[boarder_punk]

Are you totally sure that it is missing and not just being bogged down by something else? If it only does it when you are driving, to me it sounds like it may possibly be related to the transmission. Check torque converter and TCC.

And if the ECT sensor voltage is off by a little bit it could cause the PCM to adjust its outputs according to false conditions, causing the engine to run kind of funny.

[sourgrout]

its a manual transmission so thats not it... I still havent found out what it is, I drive it but it drives me nuts.