1989 G30 van idle/engine light concern?

I drive a 1989 chev G30 1 ton van. Two concerns, first after driving for 20mins or so and coming to a light and stopped the idle will surge and push the truck forward. Second concern while driving the engine light flicks on and off and causes the truck to lose power when light is on and then when light goes off power comes back, this concern just started. I had replaced IAC and TPS but did not correct concern, any help will be helpfull, thank-you.

What about an intake gasket leak. Those throttle body injection systems are notorious for leaking. My '87/G20/5.7 developed a major leak and the idle would stay up high. It would drive about 15/20 mph on a flat road without touching the accelerator. To find a leak you just need to idle the engine with the dog house off. Pull the air cleaner housing off too so you have good access to the throttle body. Listen around the base of the tb. You might be able to hear the leak. Spray carb/throttle body cleaner all around the base of the tb and if there is a leak it will get sucked in and slow the engine down momentarily. The gaskets are very easy to replace. When I took my tb off there was only a small portion of the gasket still there. I guess pieces of it got sucked into the engine and burned up. Good luck. I don't know if that will set the check engine light but it's a start. You gotta get a code reader/scan tool to figure that out. Or if it will stay on you can use a cheap paper clip or jumper to get the light to flash the code on the dash.

Have you checked your codes, you can get a little tool for a buck or two to short out the proper pins on the diagnostic plug below dash near the steering wheel. Shorting out pins A and B will give engine diagnostics, A and H will give ABS diagnostics, ect. (at least on my 94 Jimmy) The codes read out on the check engine light starting with a 12 Flash----Flash Flash repeated 3 times 12 is OK everything else is not. Ask at the car parts store for a code tool it looks like a little pickle fork with tines at the appropriate space to fit into the plug.
It's probably not your problem, but when did you replace the O2 sensor last, if it's been over 50K Mi, change it, it could be giving your injectors a lot of bad info.
Let us know what you find
94

Have you checked your codes, you can get a little tool for a buck or two to short out the proper pins on the diagnostic plug below dash near the steering wheel. Shorting out pins A and B will give engine diagnostics, A and H will give ABS diagnostics, ect. (at least on my 94 Jimmy) The codes read out on the check engine light starting with a 12 Flash----Flash Flash repeated 3 times 12 is OK everything else is not. Ask at the car parts store for a code tool it looks like a little pickle fork with tines at the appropriate space to fit into the plug.
It's probably not your problem, but when did you replace the O2 sensor last, if it's been over 50K Mi, change it, it could be giving your injectors a lot of bad info.
Let us know what you find
94
Ok I had a GM tech at a dealership take a look, it cost me $150.00 for the codes, the codes where cat converter, idle issue and no communcation with ecm. There where more interested in changing the throttlebody, the tech said it had play in shaft. After that I said see you later, the throttlebody is a re-built GM napa unit, only 8 months old. I took it and had the cat converter changed and I installed a new bosch O2 sensor. The engine light was not on solid but would flash from time to time and idle would go up and down alot when at a stop. After driving for a week, I was at a coffee shop and this guy liked my truck, just re-painted and undercarrige sand blasted and painted, he was driving a 90 gmc 2500 G-van. I was telling him my problem and he told me where to get fixed. I thought why not, I wnt there and meet the tech<small garage>, after 2 hours it was fixed. The wiring running under the floor to the ecm was damaged and the ecm could not always have a good communcation with TPS sensor. It cost me $150.00 including tax, it has been more than two weeks now and works great, it is great when you find a tech who knows Chev or gmc vans and owned one.

Glad to hear the happy ending. Sounds like you got taken at that first stop. Good thing you got out when you could.