yet another surging idle problem!!!

rnj · 10-28-2006, 10:53 PM

ok folks, please HELP!!!! I have a 92 brew 5.7 7r4 trans 16?,??? miles. Have had fuel pump/filter spark plugs replaced iac, air temp, o2 sensores repaleced. tried a new map sensor, and still surging, but just at idle. it surges from 750-1100 rpm. What else can it bee. I've checked for vac. leaks. but have not found any. I replaced the map last, when I was fiddling around, I unplugged the old map sensor and the idle was normal, so i replaced it, but it didn't resolve. I should add that the ac clutch went out, but comp. spins, could that have anything to do with the idle prob??? any info, will be greatly appreciated!!!!

rhandwor · 10-31-2006, 08:43 PM

Check the throttle position sensor these will give erratic idle. Watch the voltage on your scanner to check what is happening.

rnj · 11-27-2006, 12:14 PM

How do you check the tps voltage???

rhandwor · 11-27-2006, 12:20 PM

My OTC 4000E will give you the voltage. If you don have a scanner make some connectors and use your DVOM. Or you can use a couple bed of nails leads on your volt ohm meter. These leads have small pin points which penetrate the cable. Use silicon to coat the leads after testing. DVOM digital volt ohm meter.

rnj · 11-28-2006, 11:20 PM

what causes the idle to be erratic on warm up??? It seems that when the car is warming up it is surging. then after a few minutes it is smooth. When I drive it, it hesitates unless I stand on the gas it takes off after a few seconds.

rhandwor · 11-29-2006, 03:47 PM

I would check terminal connections at MAF,idle air control,t-p sensor,
Did you check distributor cap and rotor. If you have a logic probe that checks for pulsating signal,5volt reference,positive,and negative. I would check the connections at the distributor. Also check for any bad hose from the air filter,to the intake. I had to clean the intake on my 5.3L pickup as it was sticky.

rnj · 11-29-2006, 09:51 PM

Thanks for the replys rhandwor, I have replaced the plugs, after that it was at the state of still surging and close to stalling, so I thought I was on the right track, before the new plugs it would not stay running. I checked the dist. cap and all of the nodes(???) had about an 1/8 of an inch of buildup on them so I changed that and same thing. When I drive the car, it feels like it's missing and when I put it into the passing gear it just seems that there is no power, and feels like it jerks a bit through 30-40mph. Would the plug wires even though they clip on nice and snug cause this? I don't recall ever having a problem with plug wires before. I will try to check voltage on the tps, and this car does not have a maf, but i did change the iat sensor

rhandwor · 11-30-2006, 04:15 PM

I used aftermarket plug wires and a lot of them I had to recrimp the ends at the spark plug.
My son's 5.7L in a 1997 GMC pickup started having these type of problems and then the fuel pump falied. When replaced the problems stopped. I would check the pressure with a gage for operating and crimp off the return to check full pump pressure. If you don't have a gage use vise grips and slowly tighten on the return at a rubber hose have some body gun the car and see if it improves.
I would use a spark plug grounded to the frame and check for a good spark.
You also could loosen the exhaust nuts before the catalic converter pull apart appx. 1 inch to check if your converter is plugged.

rnj · 11-30-2006, 08:34 PM

thanks again for the input. the fuel pump was replaced first. but that did not solve the surging. the fuel pump is about 4 maybe 5 month old. the cat. was replaced last winter, but I was wondering if it may be clogged. I tuned-up only the plug cap and rotor, you think a wire maybe bad? I've been reading some relatively related issues with acceleration, stalling and hard starts and i keep seeing purge canister solinoid, and egr/ egr solenoid could 1 of these cause the surging? and I had the car at a mechanic and he checked the cts voltage and said that it was operating normal. I need to get it tested for emissions, but I know it won't pass. Will the results help in pointing in the right direction?

rhandwor · 11-30-2006, 08:48 PM

These vehicles have a fuel dist. with a pressure regulator if you look along the manifold it is cast iron about 2 inchs by 4 inchs. They put the regulator on the inside so you have to remove the upper plenium chamber to replace. If you can pull the vacuum hose with a long needle nose check for fuel in it. This is why I suggested clamping the return hose with needle nose channel locks. If bad the car should have more power. Using a pressure gage is best.
The emissions test will give you all codes. Auto zone will scan your engine for codes free. Walmart sells a scanner for $68.00. I would use an ohm meter to check all plug wires. Was your rotor replaced with the cap.
Pinch off the vacuum hose to the brake vacuum booster they sometimes cause problems. If you have a haynes follow instructions to ohm the coil.
Use a volt meter put 12 volt on the positive the negative should be 11 plus volt. Disconnect the neg when doing this.
Also ohm the temp. sensor if it is over 7000 ohms ohm a new one at a parts store. A grounded unit will cause problems.

rnj · 12-01-2006, 10:41 AM

I don't have tpi, it is tbi. But i'm going to test the coil and wires. I didn't even think about testing the wires, but I already intened to test the coil, tks!!! I'll try tonight and post back. I'm going to test the car for emissions in the morning realy doubt it will pass, but i'm interested to see the results.

rhandwor · 12-01-2006, 01:01 PM

If its throttle body injected you can try to enrich the mixture with starting fluid if it smooths out it is a fuel problem. Gun the engine while spraying if it works a lot better it is a fuel problem. The pressure regulator is under the back of the throttle body. They sell rebuild kits for them. Splice a tee in the fuel line and install a pressure gage.Better buy a pressure gage with a fitting you can screw onto the gage mounting valve. You can use fittings where it screws into the throttle body. A lot of these throttle bodies get dirty and need cleaned out. You can buy a kit like a carb. kit. I have pulled them off and cleaned all openings with carb. cleaner. Auto zones yellow can is a good one.
Gum out is about 30% of what it used to be.
The egr valve on these engines cause a rough idle when leaking. You can get on a hill and the engine shakes. Try plugging the hose to the egr with a small bolt. Also check if its leaking through. Clean it out real good and lube the shaft with spray greese. Use a vacuum gage and check that it gets vacuum when the engine is gunned. Sorry I was thinking you had a newer design engine.

rnj · 12-01-2006, 02:57 PM

that is ok, I'm just happy to be getting a response. the car has been like this since july.

rnj · 12-01-2006, 11:59 PM

Maybe this will help, or not. The tempurature here dropped down to low 20's. I didn't get a chance to mess with the car, but I thought I would start it to see how it would react in this cold weather. When it started the idle dropped once right away, but recovered and seemed to run normal cold idle.

It ran fine for about five minutes then started the surging, but never stalled. What do you make of that.

rhandwor · 12-02-2006, 07:50 AM

When the temp drops the fuel mixture is a lot richer. I would get a can of carb. cleaner. Spray around the edges of the intake manifold and around the base of the throttle body. Check pcv valve hoses and other vacuum hoses for leaks. If you have an intake leak the engine will smooth out when the spray hits it. I had a friend with a big motor in a chevy and he went to the junk yard and bought two injectors from a 305. This caused the same problem you have. When starting fluid was sprayed into the throttle body it smoothed right out. He then had to buy two injectors from a 5.7L throttle body.
Try unplugging the temp. sensor and see what happens.

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