Hi, I have a 85 z28 5.0 FI. I just got it about two weeks ago and I need some help. I have tried just about everything I can think of and I'm still having the same problem. When cold, the car will start but I have to stay on the gas and I can hear it spitting out through the intake. It runs fine when it is warm except that when I let off the gas, the car will not decelerate. It will stay at whatever speed I let off at which is not too big of a deal (it's like cruise control). Then when I put it in park, it will rev to about 2000 rpm's. If I shut it off and then back on, it will run fine at about 850 then slowly start to climb back to 2000, then drop down and go back up again.

The SES light will come on at lower speeds. When I went to get the codes the only one I got was three quick flashes then back to code 12 (but I'm not sure what those three quick flashes mean). I do know that I have changed the IAC, cleaned the TB and checked for vacuum leaks (of which there are none). I have 5.0 volts at the TPS, I pulled the MAF and the car shuts off so I assume it's good. I also changed the coolant temp sensor. I've run out of ideas and I really just want the car to run. I'm not sure if not having a fan relay would have anything to do with any of this (the guy who had it before me just hard wired it) but I'm waiting on the relay to come in. Thanks for any help.

 

Do a search for "idle too fast" and "IAC". There are tons of posts on here that address your problem. Search button is at the top of the page.

 

Thank you i have looked threw them and nothing has quit the same problem i did the whole iac reset and tps adjustment and nothing has change do you think this is a good sign that the ecm is going bad

 

It's a possibility. "Limp home" mode isn't always the same for every car. I've never heard of the throttle sticking due to a dead ecm. The revving however is a symptom. The fan relay shouldn't be causing the problem. The three quick flashes are another issue. Code 47 or 55 usually indicate ecm failure, but if it's dead you may not get anything. there is no 3 code. I know you said you checked for vacuum leaks, but did you check the vacuum line that plugs in under the throttle body? It can be loose and not be obvious.

One more thing. Can you check the code again and make sure it's not code 32? That's your EGR.

 

Alright i got the codes it gave me 14,15,22,33,44 not realy sure what this could mean but it is alot of codes i have a new alt but the gauge has been acting up maybe something acting crazy and drawling to much current not sure what is your suggestions

 

Looks like you've got all kinds of fun stuff going on. You'll notice that some of your codes contradict each other. When something is reading high and low generally means it is the problem not indicative of a problem. 14 and 15 represent this. Change your coolant sensor. It's easy and cheap. Be warned though. You will lose coolant when you take that sucker out so be prepared. Also, only make one change at a time. don't try to fix all of the codes at once. Make a change, clear the codes, start her up and see what happens. You might be surprised what magically stops being a problem. BTW code 33 won't fix itself. You've got a vacuum leak somewhere.

Here is the dictionary:

TROUBLE CODES
12. No reference pulses to Electronic Control Module (ECM).
13. Oxygen sensor signal stays lean during warm engine cruise
14. High temperature indicated at engine coolant temp sensor
15. Low temperature indicated at engine coolant temp sensor
16. High battery voltage OR Direct inition system open or shorted to ground
17. RPM signal problem
18-20. N/A
21. High voltage at throttle positon sensor
22. Low voltage at throttle positon sensor OR Fuel cutoff relay circuit open or shorted to ground
23. Low temperature at manifold air temperature sensor OR Throttle position sensor error
24. Circuit fault in vehicle speed sensor
25. High temperature at manifold air temperature sensor OR Vacuum switching valve circuit open or shorted to ground OR High voltage at ATS sensor
26. Fault in quad driver module
27. Fault in 2nd gear switch
28. Fault in 3rd gear switch
29. Fault in 4th gear switch
30. N/A
31. Low voltage at manifold absolute pressure sensor OR Fuel injector OR Park or neutral switch OR CAM diagnostic OR Governor malfunction OR Wastegate overboost OR Wastegate eletrical signal open or shorted to ground
32. Fault in barometric pressure sensor circuit OR Fault in exhaust gas recirculation valve diagnostic switch OR Fault in electronic vacuum regulator valve
33. High voltage (low vacuum) at mass air flow sensor (or MAP sensor)
34. Low voltage (high vacuum) at mass air flow sensor (or MAP sensor)
35. Idle speed can not be set to desired RPM
36. Burn off at mass air flow sensor OR Problem in transmission shift OR Fault in direct ignition system OR Missing pulses in electronic spark timing signal
37. N/A
38. Fault in torque converter clutch brake switch
39. Fault in torque converter clutch circuit
40. N/A
41. Fault at cam sensor OR Cylinder select error OR Tach input error
42. Fault at electronic spark timing circuit OR Fault at direct ignition system OR Fault at fuel cutoff relay circuit
43. Low voltage at electronic spark timing circuit
44. Oxygen sensor lean
45. Oxygen sensor rich
46. Fault at vehicle anti-theft sytem OR Fault at power steering switch
47. Problem at Electronic Control Module (ECM)
48. Misfire
49. Vacuum leak
50. N/A
51. PROM error
52. Problem at Electronic Control Module (ECM) - Missing fuel calpac missing OR Analog to digital converter error OR Fault at quad driver module OR Low voltage at oil temperature sensor
53. High voltage at battery OR High voltage at exhaust gas recirculation valve OR Voltage reference error OR Problem at vehicle anti-theft system
54. Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module
55. Problem at Electronic Control Module (ECM) - ECM failure OR Serial bus error OR Fuel lean malfunction
56. Low coolant or corrosivity OR Fault in port throttle system vacuum sensor
57. N/A
58. Problem at vehicle anti-theft system
59-60. N/A
61. Oxygen sensor degraded OR Port throttle system error OR Cruise control problems
62. Gear switch input diagnostics OR High voltage at oil temperature sensor OR Fault in cruise control- vacuum solenoid circuit
63. High voltage at manifold absolute pressure sensor OR Fault in exhaust gas recirculation valve OR Fault at right oxygen sensor
64. Low voltage at manifold absolute pressure sensor OR Fault in exhaust gas recirculation valve OR Right oxygen sensor lean
65. Failure at exhaust gas recirculation valve OR Faulure at injector peak/hold diagnostic OR Right oxygen sensor rich OR Fault at cruise control position sensor

66. Internal reset of Electronic Control Module (ECM)
67. Fault at cruise control switch
68. Fault at cruise control switch
69. Fault at air conditioner pressure switch
70-87. N/A
88. Internal reset of Electronic Control Module (ECM)

 

Yeah alright i pulled the top part of the intake off sealed up the egr fixed a vacuume line that was cracked fixed the heater core car runs great now changed the coolent temp as well the only thing i have left to do is the fan relay came in hooked it up and nothing checked the fuse it was good so i have to track the bad wire somewhere if you have any ideas on that let me know

 

The wire that goes from the fan relay to the fans can get pretty corroded. Mine was pretty bad. When I pulled it out to check the condition, it fell apart. It sits pretty close to the manifold/headers so it really takes a beating from the heat. I spliced in a new piece about a foot long and rerouted it away from the exhaust. Hope this helps.

PS. Don't want to sound obvious but make sure you use auto grade wire and inline connectors. Autozone and Advance Auto always have them in stock. I also ran the wire through some plastic flex tube just to be safe and it looks better too.

 

My fan relay is located by the batt the guy who had it before me hard wired the fan to a switch the plug is in good shape but he removed the fuse for it when i put the new one in the fan will now cut on when you turn the key when its cold with out the relay when its warm the relay seems to do nothing is there another relay by the headers

 

Sorry about that. I used the wrong term. I meant sensor not relay. I've got a 87 with a 5.7 so you might not have exactly the same setup. On mine, there is a temp sensor on the passenger side of the block between the back two cylinders. That is your fan control switch. It should connect to the relay instead of the being hardwired.

 

Hi, not sure if this has been addressed as I am lazy and only really skimmed through this thread(sorry), but the TPS should not be 5.0 volts. You should adjust the TPS so you get a reading of .54 volts give or take a little. The TPS can cause various issues if it is not adjusted properly or if it has gone bad. Hope this helps.