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1994 Bravada idle/driveability problems

03-13-2008, 09:21 AM
OK, here is the problem(s). A month ago I had cold start problems with my Bravada (4.3 Vortec). Fuel Pressure Test indicated a rapid leakdown from 60 psi to 0 psi. The Auto Repair Shop replaced the 'spider' assembly and everything was fine for a week. Same problem occurs a week later and they replaced the fuel pump/filter. The cold start problem has been fixed, but here's my new problems:

1. Erratic Idle when cold. Acts like it wants to stall, but idle increases, then decreases. This doesn't occur when the vehicle has warmed up.

2. When the A/C is switched on the idle drops like it wants to stall, then increases to normal RPM. This occurs anytime the A/C clutch engages/disengages.

3. Driveability: during deaccel (coming to a stop) the engine tends to surge for a second (increases RPM).

4. Gas Mileage has decreased from 16 to 10 mpg.

I will take the vehicle back to the shop to have them fix this right; I was just wondering if they screwed something up when replacing the 'spider' assembly? Any suggestions would help.

Chris Stewart
03-13-2008, 11:34 AM
You should have a Check Engine light on.
Your symptoms could be an ignition coil going bad, heated O2 sensor problem, sticking Idle Air Control valve (IAC) and/or EGR valve sticking open (incorrect pintle position)...
It needs a tune-up.
Not really connected to the work performed you described but many do this work when the plenum is opened, there's a fuel supply line and a fuel return line connected to the CPI "spider" that in time develope cracks and can leak raw fuel inside the intake plenum...GM calls it a "nut kit" for reasons known only to GM. These also show similiar problems when they start leaking and the leak can get so bad that raw fuel will wash down the cylinder walls, delute the motor oil and ruin the crankshaft & bearings pretty quick. Replacement of these fuel lines solves the problem.
It's good you're attending to the problem in a timely fashion.

03-13-2008, 03:02 PM
Chris, thanks for the response.
No the Check Engine Light is not on. Would the OBD 'spit' out any codes by chance?
When the 'spider' assembly was replaced, the fuel supply and return lines were supposedly replaced.

You mentioned the Ign. coil, IAC valve, O2 sensor, EGR valve. If any of these had a problem, would the drivability only be affected at cold temp. or throughout the whole temperature range?

Sorry, for all the questions; I'm just trying to narrow this down.

Chris Stewart
03-14-2008, 12:25 AM
The ignition coil will slowly get worse after the motor is warm. Everything else can cause run problems regardless of temperature.
The '94 Bravada OBD is a mix of I and II. I don't know the particulars except a regular scan tool or the OBDI paperclip access isn't likely to work.
Maybe it might show pending codes like a regular OBDII with the compatable scan tool(???)
One of the most common issues is the sticking pintle on the EGR valve. A piece of carbon from the exhaust can hold the pintle( a little plug type valve) open during cold and idle conditions causing poor idle. There's an EGR screened gasket to keep the carbon chunks out.

I think Eric's had bad bearings in his distributor which made his miss too.

How long since the last tune-up replacing plugs, wires, rotor button & distributor cap?

03-14-2008, 08:38 PM
Yes, I had simular problems and the first thing I did was replace the spider and fuel lines to. They really need to be changed but didn't fix the problem. Went back to trouble shooting it as an ignition problem and found a bad distributor bearing. If they take off the plenum to inspect the spider, that's the time to inspect the distributor while you can see it.

03-14-2008, 11:08 PM
Did yours Idle/Misfire bad only when cold or all the time? Was the vehicle getting terrible gas mileage?

Yes, it probably needs a cap/rotor replacement and spark plug/wire change.

On a side note, I took off the cylindrical looking 'manifold valve' off the intake to look inside the plenum, and it did look and feel slightly wet inside the plemnum and smelled like fuel.
Also, I've noticed that it takes forever for the engine to get to operating temp. (80+ degrees here in Phoenix)....stuck thermostat possibly. Don't know if it's related to any of the forementioned problems or not.
Thanks again guys.

03-15-2008, 05:03 PM
The problem grew over a year, much worse when cold. Misfire finaly got so bad raw fuel was being pumped thru and it eventualy set a 45 trouble code for rich exhaust before I took it out of service until the problem was found.

I think Chris is on the right track, change out all the usual ignition parts like rotor, cap, wires and plugs if you can't remeber when they were last changed to eliminate the easy stuff first. And use AC-Delco only, I've heard of lots of problems with after market products.

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